Compositions and methods for the delivery of nitric oxide

ABSTRACT

H-NOX proteins are mutated to exhibit improved or optimal kinetic and thermodynamic properties for blood gas NO delivery. The engineered H-NOX proteins comprise mutations that impart altered NO or O 2  ligand-binding relative to the corresponding wild-type H-NOX domain, and are operative as physiologically compatible mammalian blood NO gas carriers. The invention also provides pharmaceutical compositions, kits, and methods that use wild-type or mutant H-NOX proteins for the treatment of any condition for which delivery of NO is beneficial.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase application under 35 USC §371 ofInternational Application No. PCT/US2007/012133, filed May 21, 2007,which claims the benefit of U.S. provisional application Ser. No.60/921,505, filed May 22, 2006 by Michael A. Marletta, Stephen P. L.Cary, Elizabeth M. Boon, and Jonathan A. Winger, entitled “EngineeringH-NOX Proteins for Therapeutic Nitric Oxide and Oxygen Delivery”. ThisU.S. provisional application was converted from U.S. utility applicationSer. No. 11/440,588, filed May 22, 2006, to a provisional application onMay 1, 2007. The entire contents of each are hereby incorporated byreference in their entireties.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This work was supported by Grant No. DE-ACO3-76SF. The U.S. governmentmay has rights in any patent issuing on this application.

TECHNICAL FIELD

This application pertains to H-NOX proteins and methods of using them todeliver nitric oxide (NO). H-NOX proteins provide a new therapeutic toolfor delivering NO to humans and, for veterinary purposes, to animals.

BACKGROUND OF THE INVENTION

NO acts as a chemical messenger in the control of many importantprocesses in vivo, including vasodilation, neurotransmission,inflammation, platelet aggregation, and regulation of gastrointestinaland vascular smooth muscle tone. Since the discovery in 1867 by Drs.Lauder Brunton and William Murrell that nitroglycerin (GTN) is capableof treating heart disease conditions such as angina pectoris, organicnitrates have been widely used to treat acute cases of vasoconstriction.Within the last several decades, the mechanism of vasodilation has beenelucidated. NO, which is synthesized in endothelial cells, diffuses tosmooth muscle cells and activates soluble guanylate cyclase (sGC) toproduce cyclic GMP, and thereby induce vasodilation. The clinicalmechanism of action of organic nitrates, then, is presumed to requiretheir biotransformation to NO and subsequent activation of sGC. However,organic nitrates cease to be effective in patients after 24-48 hours,due to a phenomenon called tolerance. Thus, for treatment of chroniccases of hypertension, compounds such as β-blockers and ACE inhibitorsare used, although they too have limitations and side effects. Thus,nitrovasodilators are most useful in treating acute situations whererapid vasodilation is required to alleviate symptoms such as angina andmyocardial infarction. Prolonged administration of organic nitratesresults in reduced efficacy, and the vasculature becomes non-responsive;this tolerance prevents their further use both in chronic and acutecases. Thus, for acute treatment, non-continuous nitrovasodilator use isemployed with limited effect. For chronic cases of vasoconstriction,other avenues of treatment are employed, typically using a mixed regimenof organic nitrates and NO-independent blood pressure medications, withmixed success.

Two major competing theories on the mechanism for tolerance run parallelto the search for the mechanism of biotransformation of nitrates thatleads to release of NO. Because NO is believed to be the mediator of thevasodilatory effects of organic nitrates, the mechanism of release of NOfrom organic nitrates may become inhibited, resulting in tolerance. Buthow organic nitrates metabolically release NO in tissues is notunderstood. Furthermore, the mechanism-based theory for tolerance isproblematic because tolerance also reduces the efficacy of endogenous NOand exogenous NO gas in mediating vasodilation. Thus, the mechanism ofbiotransformation of organic nitrates appears to be separate from thereason for tolerance. A competing theory posits that the response to NOfrom organic nitrates becomes dampened in the target tissue, perhapsbecause the generation of NO and the by-products of the reactioneventually inhibit the response to NO, or because acute activation ofthe NO pathway has a feedback mechanism that desensitizes it to furtherstimulation. This theory is known as end-organ tolerance. Recently, aunifying theory has been proposed that includes aspects of thebiotransformation of organic nitrates as well as end-organdesensitization to NO. Essentially, biotransformation of organicnitrates appears to result in higher levels of superoxide (O₂ ⁻) intissues. Superoxide reacts at the rate of diffusion with NO to produceperoxynitrite (OONO). This reaction essentially traps and destroys basalNO, preventing it from activating sGC. Reduced NO levels leads tovasoconstriction, and OONO⁻ is a powerful oxidant that damages tissues.Prolonged treatment with organic nitrates such as GTN can result inhypertension and tissue damage in patients, and this can be moderatedwith co-administration of antioxidants such as ascorbate. Thus, improvedtherapeutics for delivering NO to organs and tissues to alleviatevasoconstriction is a major therapeutic goal.

Some research has been conducted on the use of hemoglobin-based carriersto deliver NO. However, hemoglobin-based carriers are limited due totheir reactivity with NO in the presence of O₂, which leads to theinactivation of hemoglobin-based carriers. NO reacts directly with O₂that is bound to hemoglobin to form methemoglobin and nitrate. Both theheme iron and NO become oxidized by the bound oxygen atoms, and thereaction occurs so rapidly that no replacement of O₂ by NO is observed(see, e.g., U.S. Pat. No. 6,455,676).

Since NO is produced and consumed on a continuous basis, there is anatural turnover of NO in vivo. When cell-free hemoglobin isadministered, the balance between NO production and consumption isaltered by reactions with cell-free hemoglobin. The oxidative reactionbetween NO and O₂ bound to hemoglobin is irreversible, resulting in thedestruction of NO, O₂, and hemoglobin. NO binding to hemoglobin withoutO₂ bound is effectively irreversible on physiologic timescales since thehalf-life for dissociation of nitrosylhemoglobin is 5-6 hours, therebyeffectively inactivating hemoglobin as a cell-free NO carrier. Once anNO molecule reacts with hemoglobin, it is eliminated from the pool ofsignal molecules, thereby causing certain adverse conditions. Forexample, the binding of NO to hemoglobin (with or without O₂ bound) canprevent vascular relaxation and potentially lead to hypertension, whichis sometimes observed after the administration of certain extracellularhemoglobin solutions.

NO is also needed to mediate certain inflammatory responses. Forexample, NO produced by the endothelium inhibits platelet aggregation.Consequently, as NO is bound by cell-free hemoglobin (with or without O₂bound), platelet aggregation may increase. As platelets aggregate, theyrelease potent vasoconstrictor compounds such as thromboxane A₂ andserotonin. These compounds may act synergistically with the reduced NOlevels caused by hemoglobin scavenging to produce significantvasoconstriction. In addition to inhibiting platelet aggregation, NOalso inhibits neutrophil attachment to cell walls, which in turn canlead to cell wall damage. Endothelial cell wall damage has been observedwith the infusion of certain hemoglobin solutions. Hemoglobin-based NOcarriers are also hindered by the rapid clearance of cell-freehemoglobin from plasma due the presence of receptors for hemoglobin thatremove cell-free hemoglobin from plasma. Cell-free hemoglobin may alsocause kidney toxicity, possibly due to NO depletion in glomeruli,causing constriction and subsequent dysfunction.

Due to the limitations of current nitrovasodilator therapies, thereremains a significant interest in and need for additional or alternativetherapies for delivering NO. In particular, NO carriers that produceless tolerance are needed. Additionally, NO carriers with a low rate ofinactivation by NO in the presence of O₂ are desired, such as NOcarriers that have a low NO reactivity and/or a low affinity for O₂. NOcarriers with NO dissociation constants or NO dissociation rates thatare appropriate for particular clinical or industrial applications arealso needed.

BRIEF SUMMARY OF THE INVENTION

The present invention is based in part on the surprising discovery thatwild-type and mutant H-NOX proteins have a much lower NO reactivity thanhemoglobin and thus are desirable NO carriers. If desired, mutations canbe introduced into H-NOX proteins to alter their binding of NO and O₂ligands to further optimize the use of H-NOX proteins as NO carriers. Insome embodiments, use of an H-NOX protein as an NO carrier produces lesstolerance than the use of current vasodilators, such as organicnitrates.

In one aspect, the invention features mutant H-NOX proteins.Accordingly, in some embodiments, the invention provides an isolatedH-NOX protein comprising at least one mutation that alters the NO,dissociation constant or NO reactivity compared to that of acorresponding wild-type H-NOX protein. In some embodiments, the NOdissociation constant of the mutant H-NOX protein is within 2 orders ofmagnitude of that of hemoglobin, and the NO reactivity of the mutantH-NOX protein is at least 10-fold lower than that of hemoglobin. In someembodiments, the NO reactivity of the mutant H-NOX protein is at least100-fold lower than that of hemoglobin, such as at least 1,000-foldlower than that of hemoglobin. In some embodiments, the k_(off), k₁, ork₂ for NO of the mutant H-NOX protein is between about 1×10⁻⁴ s⁻¹ toabout 10 s⁻¹ at 37° C., such as about 1×10⁻⁴ s⁻¹ to about 0.012 or about1×10⁻⁴ s⁻¹ to about 1×10⁻³ s⁻¹ at 37° C. In some embodiments, the O₂dissociation constant of the mutant H-NOX protein is at least about 1 μMat 37° C., such as at least about 10 μM or at least about 50 μM at 37°C.

In some embodiments, the invention provides an isolated H-NOX proteincomprising at least one mutation that alters the k_(off), k₁, or k₂ forNO or alters the O₂ dissociation constant compared to that of acorresponding wild-type H-NOX protein. In some embodiments, the k_(off),k₁, or k₂ for NO of the mutant H-NOX protein is between about 1×10⁻⁴ s⁻¹to about 10 s⁻¹ at 37° C., and the O₂ dissociation constant of themutant H-NOX protein is at least about 1 μM at 37° C. In someembodiments, the k_(off), k₁, or k₂ for NO of the mutant H-NOX proteinis between about 1×10⁻⁴ s⁻¹ to about 0.012 s⁻¹ or about 1×10⁻⁴ s⁻¹ toabout 1×10⁻s⁻¹ at 37° C. In some embodiments, the O₂ dissociationconstant of the mutant H-NOX protein is at least about 10 μM, such as atleast about 50 μM at 37° C. In some embodiments, the NO reactivity ofthe mutant H-NOX protein is at least 10-fold lower than that ofhemoglobin, such as at least 100-fold lower than that of hemoglobin orat least 1,000-fold lower than that of hemoglobin.

In some embodiments, the invention provides an isolated H-NOX proteinselected from the group consisting of T. tengcongensis H-NOX I5A, T.tengcongensis H-NOX I5L, T. tengcongensis H-NOX I5L-P115A, T.tengcongensis H-NOX W9F, T. tengcongensis H-NOX W9F-Y140L, T.tengcongensis H-NOX W9F-Y140H T. tengcongensis H-NOX W9F-N74A, T.tengcongensis H-NOX W9Y, T. tengcongensis H-NOX W9N, T. tengcongensisH-NOX W9H, T. tengcongensis H-NOX N74E, T. tengcongensis H-NOX N74A, T.tengcongensis H-NOX N74H, T. tengcongensis H-NOX N74A-Y140H, T.tengcongensis H-NOX F78Y-Y140F, T. tengcongensis H-NOX P115A, T.tengcongensis H-NOX R135Q, T. tengcongensis H-NOX Y140F, T.tengcongensis H-NOX Y140H, T. tengcongensis H-NOX Y140A, T.tengcongensis I75F-His6, T. tengcongensis I75F, T. tengcongensisL144F-His6, T. tengcongensis L144F, L2 F9W-F142Y, D. desulfuricansH-NOX(728-899), D. desulfuricans H-NOX Y139L, β1(1-385), β1(1-385)I145Y, β1(1-385) I145H, β1(1-194), β1(1-194) I145Y, β1(1-194) L9W-I145Y,β2(1-217), β2(1-217), I142Y, C. botulimun H-NOX(1-175), C. botulinumH-NOX(1-186), C. acetobutylicum H-NOX(1-197), C. acetobutylicumH-NOX(1-183), and C. elegans H-NOX GCY-35(1-252). In some embodiments,the β1 or β2 protein is derived from a R. norvegicus or H sapiens β1 orβ2 protein.

In some embodiments, the invention provides an isolated H-NOX proteinselected from the group consisting of T. tengcongensis H-NOX I5A, T.tengcongensis H-NOX I5L, T. tengcongensis H-NOX I5L-P115A, T.tengcongensis H-NOX W9F-Y140L, T. tengcongensis H-NOX W9F-Y140H, T.tengcongensis H-NOX W9F-N74A, T. tengcongensis H-NOX W9Y, T.tengcongensis H-NOX W9N, T. tengcongensis H-NOX W9H, T. tengcongensisH-NOX N74E, T. tengcongensis H-NOX N74A, T. tengcongensis H-NOX N74H, T.tengcongensis H-NOX N74A-Y140H, T. tengcongensis H-NOX F78Y-Y140F, T.tengcongensis H-NOX P115A, T. tengcongensis H-NOX R135Q, T.tengcongensis H-NOX Y140H, T. tengcongensis H-NOX Y140A, T.tengcongensis I75F-His6, T. tengcongensis I75F, T. tengcongensisL144F-His6, T. tengcongensis L144F, L. pneumophilia 2 F9W-F142Y, D.desulfuricans H-NOX(728-899), D. desulfuricans H-NOX Y139L, β1(1-385)I145H, β1(1-194), β1(1-194) I145Y, β1(1-194) L9W-I145Y, β2(1-217),β2(1-217) I142Y, C. botulinum H-NOX(1-175), C. botulinum H-NOX(1-186),C. acetobutylicum H-NOX(1-197), C. acetobutylicum H-NOX(1-183), and C.elegans H-NOX GCY-35(1-252). In some embodiments, the β1 or β2 proteinis derived from a R. norvegicus or H. sapiens β1 or β2 protein.

In some embodiments of the isolated H-NOX proteins, the NO dissociationconstant of the H-NOX protein is between 0.1 to 10-fold of that ofhemoglobin, such as between 0.5 to 2-fold of that of hemoglobin. In someembodiments of the isolated H-NOX proteins, the NO dissociation constantof the H-NOX protein is within 2 orders of magnitude of that of Homosapiens hemoglobin alpha, such as an NO dissociation constant between0.1 to 10-fold or between 0.5 to 2-fold of that of Homo sapienshemoglobin alpha. In some embodiments of the isolated H-NOX proteins,the NO reactivity of the H-NOX protein is at least 10-fold lower thanthat of Homo sapiens hemoglobin alpha, such as at least 100-fold or1,000-fold lower than that of Homo sapiens hemoglobin alpha. In someembodiments of the isolated H-NOX proteins, the NO reactivity of theH-NOX protein is less than about 700 s⁻¹ at 20° C., such as less thanabout 600 s⁻¹, 500 s⁻¹, 400 s⁻¹, 300 s⁻¹, 200 s⁻¹, 100 s⁻¹, 75 s⁻¹, 50s⁻¹, 25 s⁻¹, 20 s⁻¹, 10 s⁻¹50 s⁻¹, 3 s⁻¹, 2 s⁻¹, 1.8 s⁻¹, 1.5 s⁻¹, 1.2s⁻¹, 1.0 s⁻¹, 0.8 s⁻¹, 0.7 s⁻¹, or 0.6 s⁻¹ at 20° C. In some embodimentsof the isolated H-NOX proteins, the O₂ dissociation constant of theH-NOX protein is at least about 1 μM at 37° C., such as at least about10 μM or at least about 50 μM at 37° C. In some embodiments of theisolated H-NOX proteins, the k_(off), k₁, or k₂ for NO of the H-NOXprotein is between about 1×10⁻⁴ s⁻¹ to about 10 s⁻¹ at 37° C., and theO₂ dissociation constant of the H-NOX protein is at least about 1 μM at37° C. In some embodiments of the isolated H-NOX proteins, the k_(off),k₁, or k₂ for NO of the H-NOX protein is between about 1×10⁻⁴ s⁻¹ toabout 10 s⁻¹ at 37° C., and the NO reactivity of the H-NOX protein isless than about 700 s⁻¹ at 20° C. (e.g., less than about 600 s⁻¹, 500s⁻¹, 100 s⁻¹, 20 s⁻¹, or 1.8 s⁻¹ at 20° C.). In some embodiments of theisolated H-NOX proteins, the O₂ dissociation constant of the H-NOXprotein is at least about 1 μM at 37° C., and the NO reactivity of theH-NOX protein is less than about 700 s⁻¹ at 20° C. (e.g., less thanabout 600 s⁻¹, 500 s⁻¹, 100 s⁻¹, 20 s⁻¹, or 1.8 s⁻¹ at 20° C.). In someembodiments of the isolated H-NOX proteins, the rate of hemeautoxidation of the H-NOX protein is less than about 1 h⁻¹ at 37° C. Insome embodiments of the isolated H-NOX proteins, the k_(off), k₁, or k₂for NO of the H-NOX protein is between about 1×10⁻⁴ s⁻¹ to about 10 s⁻¹at 37° C., and the rate of heme autoxidation of the H-NOX protein isless than about 1 h⁻¹ at 37° C. In some embodiments of the isolatedH-NOX proteins, the O₂ dissociation constant of the H-NOX protein is atleast about 1 μM at 37° C., and the rate of heme autoxidation of theH-NOX protein is less than about 1 h⁻¹ at 37° C. In some embodiments ofthe isolated H-NOX proteins, the rate of heme autoxidation of the H-NOXprotein is less than about 1 h⁻ at 37° C., and the NO reactivity of theH-NOX protein is less than about 700 s⁻¹ at 20° C. (e.g., less thanabout 600 s⁻¹, 500 s⁻¹, 100 s⁻¹, 20 s⁻¹, or 1.8 s⁻¹ at 20° C.).

In some embodiments of the isolated H-NOX proteins, the H-NOX proteincontains one or more mutations (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10mutations) compared to the H-NOX protein from which it was derived. Invarious embodiments, the H-NOX protein contains less than 20, 15, 12,10, 9, 8, 7, 6, 5, 4, 3, or 2 mutations compared to the H-NOX proteinfrom which it was derived. In some embodiments, the H-NOX protein has atleast one distal pocket mutation. In some embodiments, the H-NOX proteinhas at least one mutation that is not in the distal pocket. In someembodiments, the H-NOX protein has at least one mutation in which aresidue that corresponds to Tyr140 of T. tengcongensis H-NOX or Phe142of L. pneumophila 2 is replaced by any other amino acid. In someembodiments, the H-NOX protein has at least two mutations, wherein atleast one mutation is the replacement of a residue that corresponds toTyr140 of T. tengcongensis H-NOX or Phe142 of L. pneumophila 2 by anyother amino acid. In some embodiments, the mutation in the H-NOX proteincorresponds to a Y140F mutation or a Y140L mutation of T. tengcongensisor a F142Y mutation of L. pneumophila 2. In some embodiments of theisolated H-NOX proteins, at least one C-terminal amino acid (such as atleast about 50 contiguous C-terminal amino acids or between about 25 toabout 200 contiguous C-terminal amino acids) in the H-NOX protein hasbeen removed compared to the corresponding wild-type protein. In someembodiments, the H-NOX protein is a deletion that contains the first194, 217, or 385 amino acids of an H-NOX protein such as R. norvegicusor H. sapiens β1 or β2 protein.

In some embodiments of the isolated H-NOX proteins, the H-NOX protein isderived from a mammalian protein (e.g., a human protein such as β1). Invarious embodiments of the isolated H-NOX proteins, the H-NOX proteinderived from a bacterial protein (e.g., a T. tengcongensis protein). Insome embodiments of the isolated H-NOX proteins, the H-NOX protein iscovalently bound to another molecule or moiety, such as polyethyleneglycol. Heme may or may not be bound to the H-NOX protein. In someembodiments of the isolated H-NOX proteins, NO is bound to the H-NOXprotein. In some embodiments of the isolated H-NOX proteins, the H-NOXprotein is a fusion protein that includes an H-NOX domain and part orall of another protein, such as albumin (e.g., human serum albumin).

In some embodiments of the isolated H-NOX proteins, the H-NOX protein isnot T. tengcongensis H-NOX Y40L, wild-type T. tengcongensis H-NOX,wild-type R. norvegicus sGC, or L. pneumophilia 2 H-NOX F142Y. In someembodiments of the isolated H-NOX proteins, the H-NOX protein is not T.tengcongensis H-NOX F78Y/Y140L. In some embodiments of the isolatedH-NOX proteins, the H-NOX protein is not wild-type L. pneumophilia 2H-NOX, wild-type H. sapiens β1 H-NOX, R. norvegicus sGC β1 H-NOX(1-385), wild-type R. norvegicus β1 H-NOX, wild-type D. melangaster β1H-NOX, wild-type D. melangaster CG14885-PA H-NOX, wild-type C. elegansGCY-35 H-NOX, wild-type N. punctiforme H-NOX, wild-type C. crescentusH-NOX, wild-type S. oneidensis H-NOX, or wild-type C. acetobutylicumH-NOX. In some embodiments of the isolated H-NOX proteins, the H-NOXprotein is not T. tengcongensis H-NOX W9F, T. tengcongensis H-NOX Y140F,R. norvegicus sGC β1 H-NOX H105G, R. norvegicus sGC β1 H-NOX H105F, R.norvegicus sGC β1 H-NOX I145Y, R. norvegicus sGC β1 H-NOX C78S, or R.norvegicus sGC β1 H-NOX C78E. In some embodiments of the isolated H-NOXproteins, the H-NOX protein is not R. norvegicus β2(1-217), R.norvegicus β1(1-194), R. norvegicus β1(1-385), or R. norvegicusβ1(1-385) I145Y. In some embodiments of the isolated H-NOX proteins, theH-NOX protein is not T. tengcongensis H-NOX W9F, T. tengcongensis H-NOXY140F, or H. sapiens β1 H-NOX (1-385) I145Y. In some embodiments of theisolated H-NOX proteins, the H-NOX protein is not T. tengcongensis H-NOXY140H, H. sapiens β1 I140Y, or H. sapiens β1 I145Y. In some embodimentsof the isolated H-NOX proteins, the H-NOX protein is not T.tengcongensis H-NOX Y40L, T. tengcongensis H-NOX F78Y/Y140L, T.tengcongensis H-NOX W9F, T. tengcongensis H-NOX Y140F, wild-type T.tengcongensis H-NOX, L. pneumophilia 2 H-NOX F142Y, wild-type L.pneumophilia 2 H-NOX, H. sapiens β1 H-NOX I140Y, H. sapiens B1 I145Y,wild-type H. sapiens β1 H-NOX, R. norvegicus sGC β1 H-NOX (1-385), R.norvegicus sGC β1 H-NOX (1-385) I145Y, R. norvegicus sGC β1 H-NOX H105G,R. norvegicus sGC β1 H-NOX H105F, R. norvegicus sGC β1 H-NOX I145Y,wild-type R. norvegicus H-NOX, wild-type D. melangaster β1 H-NOX,wild-type D. melangaster CG14885-PA H-NOX, wild-type C. elegans GCY-35H-NOX, wild-type N. punctiforme H-NOX, wild-type C. crescentus H-NOX,wild-type S. oneidensis H-NOX, or wild-type C. acetobutylicum H-NOX. Insome embodiments of the isolated H-NOX proteins, the H-NOX protein isnot any of the following H-NOX proteins that are listed by their genename, followed by their species abbreviation and Genbank Identifiers(such as the following protein sequences available as of May 21, 2006;May 22, 2006; May 21, 2007; or May 22, 2007): Npun5905_Npu_(—)23129606,alr2278_Ana_(—)17229770, SO2144_Sone_(—)24373702,Mdeg1343_Mde_(—)23027521, VCA0720_Vch_(—)15601476,CC2992_Ccr_(—)16127222, Rsph2043_Rhsp_(—)22958463 (gi:46192757),Mmc10739_Mcsp_(—)22999020, Tar4_Tte_(—)20807169,Ddes2822_Dde_(—)23475919, CAC3243_Cac_(—)15896488,gcy-31_Ce_(—)17568389, CG14885_Dm_(—)24647455, GUCY1B3_Hs_(—)4504215,HpGCS-beta1_Hpul_(—)14245738, Gyebeta100B_Dm_(—)24651577,CG4154_Dm_(—)24646993 (gi:NP_(—)650424.2, gi:62484298),gcy-32_Ce_(—)13539160,gcy-36_Ce_(—)17568391 (gi:32566352, gi:86564713),gcy-35_Ce-17507861 (gi:71990146), gcy-37_Ce_(—)17540904 (gi:71985505),GCY 1α3_Hs_(—)20535603, GCY 1α2-Hs_(—)899477, or GYCα-99B_Dm_(—)729270(gi:68067738) (Lakshminarayan et al. (2003). “Ancient conserved domainsshared by animal soluble guanylyl cyclases and bacterial signalingproteins,” BMG Genomics 4:5-13). The species abbreviations used in thesenames include Ana—Anabaena Sp; Ccr—Caulobacter crescentus;Cac—Clostridium acetobutylicum; Dde—Desulfovibrio desulfuricans;Mcsp—Magnetococcus sp.; Mde—Microbulbifer degradans; Npu—Nostocpunctiforme; Rhsp—Rhodobacter sphaeroides; Sone—Shewanella oneidensis;Tte—Thermoanaerobacier tengcongensis; Vch—Vibrio cholerae;Ce—Caenorhabditis elegans; Dm—Drosophila melanogaster;Hpul—Hemicentrotus pukherrimus; Hs—Homo sapiens. In some embodiments ofthe isolated H-NOX proteins, the H-NOX protein is not any of thefollowing H-NOX proteins that are listed by their organism name and Pfamdatabase accession number (such as the following protein sequencesavailable as of May 21, 2006; May 22, 2006; May 17, 2007; May 21, 2007;or May 22, 2007): Caenorhabditis briggsae Q622M5_CAEBR, Caenorhabditisbriggsae Q61P44_CAEBR, Caenorhabditis briggsae Q61R54_CAEBR,Caenorhabditis briggsae Q61V90_CAEBR, Caenorhabditis briggsaeQ61A94_CAEBR, Caenorhabditis briggsae Q60TP4_CAEBR, Caenorhabditisbriggsae Q60M10_CAEBR, Caenorhabditis elegans GCY37_CAEEL,Caenorhabditis elegans GCY31_CAEEL, Caenorhabditis elegans GCY36_CAEEL,Caenorhabditis elegans GCY32_CAEEL, Caenorhabditis elegans GCY35_CAEEL,Caenorhabditis elegans GCY34_CAEEL, Caenorhabditis elegans GCY33_CAEEL,Oryzias curvinotus Q7T040_ORYCU, Oryzias curvinotus Q75 WF0_ORYCU,Oryzias latipes P79998_ORYLA, Oryzias latipes Q7ZSZ5_ORYLA, Tetraodonnigroviridis Q4SW38_TETNG, Tetraodon nigroviridis Q4RZ94_TETNG,Tetraodon nigroviridis Q4S6K5_TETNG, Fugu rubripes Q90VY5_FUGRU, Xenopuslaevis Q6INK9_XENLA, Homo sapiens Q5T8J7_HUMAN, Homo sapiensGCYA2_HUMAN, Homo sapiens GCYB2_HUMAN, Homo sapiens GCYB 1_HUMAN,Gorilla gorilla Q9N193_(—)9PRIM, Pongo pygmaeus Q5RAN8_PONPY, Pantroglodytes Q9N192_PANTR, Macaca mulatta Q9N194_MACMU, Hylobates larQ9N191_HYLLA, Mus musculus Q8BXH3_MOUSE, Mus musculus GCYB1_MOUSE, Musmusculus Q3UTI4_MOUSE, Mus musculus Q3UH83_MOUSE, Mus musculusQ6XE41_MOUSE, Mus musculus Q80YP4_MOUSE, Rattus norvegicus Q80WX7_RAT,Rattus norvegicus Q80WX8_RAT, Rattus norvegicus Q920Q1_RAT, Rattusnorvegicus Q54A43_RAT, Rattus norvegicus Q80WY0_RAT, Rattus norvegicusQ80WY4_RAT, Rattus norvegicus Q8CH85_RAT, Rattus norvegicus Q80WY5_RAT,Rattus norvegicus GCYB1_RAT, Rattus norvegicus Q8CH90_RAT, Rattusnorvegicus Q91XJ7_RAT, Rattus norvegicus Q80WX9_RAT, Rattus norvegicusGCYB2_RAT, Rattus norvegicus GCYA2_RAT, Canis familiaris Q4ZHR9_CANFA,Bos taurus GCYB1_BOVIN, Sus scrofa Q4ZHR7_PIG, Gryllus bimaculatusQ59HN5_GRYBI, Manduca sexta O77106_MANSE, Manduca sexta O76340_MANSE,Apis mellifera Q5UAF0_APIME, Apis mellifera Q5FAN0_APIME, Apis melliferaQ6L5L6_APIME, Anopheles gambiae str PEST Q7PYK9_ANOGA, Anopheles gambiaestr PEST Q7Q9W6_ANOGA, Anopheles gambiae str PEST Q7QF31_ANOGA,Anopheles gambiae str PEST Q7PS01_ANOGA, Anopheles gambiae str PESTQ7PFY2_ANOGA, Anopheles gambiae Q7KQ93_ANOGA, Drosophila melanogasterQ24086_DROME, Drosophila melanogaster GCYH_DROME, Drosophilamelanogaster GCY8E_DROME, Drosophila melanogaster GCYDA_DROME,Drosophila melanogaster GCYDB_DROME, Drosophila melanogasterQ9VA09_DROME, Drosophila pseudoobscura Q29CE1_DROPS, Drosophilapseudoobscura Q296C7_DROPS, Drosophila pseudoobscura Q296C8_DROPS,Drosophila pseudoobscura Q29BU7_DROPS, Aplysia californica Q7YWK7_APLCA,Hemicentrotus pulcherrimus Q95NK5_HEMPU, Chlamydomonas reinhardtii,Q5YLC2_CHLRE, Anabaena sp Q8YUQ7_ANASP, Flavobacteria bacterium BBFL7Q26GR8_(—)9BACT, Psychroflexus torquis ATCC 700755 Q1VQE5_(—)9FLAO,marine gamma proteobacterium HTCC2207 Q1YPJ5_(—)9GAMM, marine gammaproteobacterium HTCC2207 Q1YTK4_(—)9GAMM, Caulobacter crescentusQ9A451_CAUCR, Acidiphilium cryptum JF-5 Q2DG60_ACICY, Rhodobactersphaeroides Q3J0U9_RHOS4, Silicibacter pomeroyi Q5LPV1_SILPO, Paracoccusdenitrificans PD1222, Q3PC67PARDE, Silicibacter sp TM1040Q3QNY2_(—)9RHOB, Jannaschia sp Q28ML8_JANSC, Magnetococcus sp MC-1Q3XT27_(—)9PROT, Legionella pneumophila Q5 WXP0_LEGPL, Legionellapneumophila Q5WTZ5_LEGPL, Legionella pneumophila Q5X268_LEGPA,Legionella pneumophila Q5X2R2_LEGPA, Legionella pneumophila subsppneumophila Q5ZWM9_LEGPH, Legionella pneumophila subsp pneumophilaQ5ZSQ8_LEGPH, Colwellia psychrerythraea Q47Y43COLP3, Pseudoalteromonasatlantica T6c Q3CSZ5_ALTAT, Shewanella oneidensis Q8EF49_SHEON,Saccharophagus degradans Q21E20_SACD2, Saccharophagus degradansQ21ER7_SACD2, Vibrio angustum S14 Q1ZWE5_(—)9VIBR, Vibrio vulnificusQ8DAE2_VIBVU, Vibrio alginolyticus 12G01 Q1VCP6_VIBAL, Vibrio sp DAT722Q2FA22_(—)9VIBR, Vibrio parahaemolyticus Q87NJ1_VIBPA, Vibrio fischeriQ5E1F5_VIBF1, Vibrio vulnificus Q7MJS8_VIBVY, Photobacterium sp SKA34Q2C6Z5_(—)9GAMM, Hahella chejuensis Q2SFY7_HAHCH, Oceanospirillum spMED92 Q2BKV0_(—)9GAMM, Oceanobacter sp RED65 Q1N035_(—)9GAMM,Desulfovibrio desulfuricans Q310U7_DESDG, Halothermothrix orenii H 168Q2AIW5_(—)9FIRM, Thermoanaerobacter tengcongensis Q8RBX6_THETN,Caldicellulosiruptor saccharolyticus DSM 8903 Q2ZH17_CALSA, Clostridiumacetobutylicum Q97E73_CLOAB, Alkaliphilus metalliredigenes QYMFQ3C763_(—)9CLOT, Clostridium tetani Q899J9_CLOTE, and Clostridiumbeijerincki NCIMB 8052 Q2WVN0_CLOBE. In some embodiments of the isolatedH-NOX proteins, the H-NOX protein does not have a mutation in the Y-S-Rmotif, which includes Tyr135, Ser137, and Arg139 of human H-NOX.

In one aspect, the invention features a recombinant nucleic acidencoding any one or more of the mutant H-NOX proteins described herein.In particular embodiments, the nucleic acid includes a segment of or theentire nucleic acid sequence of any of the nucleic acids shown in FIG.2-4D or 8A-8DD. In some embodiments, the nucleic acid encodes a fusionprotein that includes an H-NOX domain and part or all of anotherprotein, such as albumin (e.g., human serum albumin). In someembodiments, the nucleic acid includes at least about any of 50, 100,150, 200, 300, 400, 500, 600, 700, 800, or more contiguous nucleotidesfrom an H-NOX nucleic acid and contains one or more mutations (e.g., 1,2, 3, 4, 5, 6, 7, 8, 9, or 10 mutations) compared to the H-NOX nucleicacid from which it was derived. In various embodiments, a mutant H-NOXnucleic acid contains less than about any of 20, 15, 12, 10, 9, 8, 7, 6,5, 4, 3, or 2 mutations compared to the H-NOX nucleic acid from which itwas derived. The invention also features degenerate variants of anynucleic acid encoding a mutant H-NOX protein.

In yet another aspect, the invention provides a vector that includes anyone or more of the mutant H-NOX nucleic acids described herein. Inanother aspect, the invention features a cell that includes any one ormore of the mutant H-NOX nucleic acids described herein. In one aspect,the invention features a cell that includes any vector described herein.

In one aspect, the invention features a method of producing an H-NOXprotein. This method involves culturing a cell having a nucleic acidencoding any one or more of the mutant H-NOX proteins described hereinunder conditions suitable for production of the mutant H-NOX protein. Insome embodiments, the invention further includes the step of purifyingthe mutant H-NOX protein.

In one aspect, the invention features pharmaceutical compositions thatinclude one or more H-NOX proteins, such as any of the wild-type ormutant H-NOX proteins described herein. In some embodiments, thepharmaceutical composition includes a pharmaceutically acceptable amountof an H-NOX protein described herein and a pharmaceutically acceptablecarrier. In some embodiments, the k_(off), k₁, or k₂ for NO of the H-NOXprotein is between about 1×10⁻⁴ s⁻¹ to about 10 s⁻¹ at 37° C., and theO₂ dissociation constant of the H-NOX protein is at least about 1 μM at37° C. In some embodiments, the NO dissociation constant of the H-NOXprotein is within 2 orders of magnitude of that of hemoglobin, and theNO reactivity of the H-NOX protein is at least 10-fold lower than thatof hemoglobin.

In some embodiments of the pharmaceutical compositions, the NOdissociation constant of the H-NOX protein is within 2 orders ofmagnitude of that of Homo sapiens hemoglobin alpha, such as an NOdissociation constant between 0.1 to 10-fold or between 0.5 to 2-fold ofthat of Homo sapiens hemoglobin alpha. In some embodiments of thepharmaceutical compositions, the NO reactivity of the H-NOX protein isat least 10-fold lower than that of Homo sapiens hemoglobin alpha, suchas at least 100-fold or 1,000-fold lower than that of Homo sapienshemoglobin alpha. In some embodiments of the pharmaceuticalcompositions, the H-NOX protein is a wild-type protein. In someembodiments of the pharmaceutical compositions, the H-NOX protein is amutant protein as described herein. In various embodiments of thepharmaceutical compositions, the H-NOX protein has at least one mutationthat alters the NO dissociation constant, the k_(off) for NO, the k₁ forNO, the k₂ for NO, the O₂ dissociation constant, the NO stability, theNO reactivity the rate of heme autoxidation, or any combination of twoor more of the foregoing compared to that of a corresponding wild-typeprotein. In some embodiments of the pharmaceutical compositions, theH-NOX protein is a selected from the group consisting of wild-type T.tengcongensis H-NOX, T. tengcongensis H-NOX I5A, T. tengcongensis H-NOXI5L, T. tengcongensis H-NOX I5L-P115A, T. tengcongensis H-NOX W9F, T.tengcongensis H-NOX W9F-Y140L, T. tengcongensis H-NOX W9F-Y140H T.tengcongensis H-NOX W9F-N74A, T. tengcongensis H-NOX W9Y, T.tengcongensis H-NOX W9N, T. tengcongensis H-NOX W9H, T. tengcongensisH-NOX N74E, T. tengcongensis H-NOX N74A, T. tengcongensis H-NOX N74H, T.tengcongensis H-NOX N74A-Y140H, T. tengcongensis H-NOX F78Y-Y140F, T.tengcongensis H-NOX F78Y/Y140L, T. tengcongensis H-NOX P115A, T.tengcongensis H-NOX R135Q, T. tengcongensis H-NOX Y140F, T.tengcongensis H-NOX Y40L, T. tengcongensis H-NOX Y140H, T. tengcongensisH-NOX Y140A, T. tengcongensis I75F-His6, T. tengcongensis I75F, T.tengcongensis L144F-His6, T. tengcongensis L144F, L. pneumophilia 2H-NOX F142Y, wild-type L. pneumophilia 1 H-NOX, wild-type L.pneumophilia 2 H-NOX, L. pneumophilia 2 F9W-F142Y, wild-type D.desulfuricans H-NOX, D. desulfuricans H-NOX(728-899), D. desulfuricansH-NOX Y139L, wild-type H. sapiens β1 H-NOX, H. sapiens β1 I140Y, H.sapiens β1 I145Y, H. sapiens β1(1-385), H. sapiens β1(1-385) I145Y, H.sapiens β1(1-385) I145H, H. sapiens β1(1-194), H. sapiens β1(1-194)I145Y, H. sapiens β1(1-194) L9W-I145Y, H. sapiens β2(1-217), H. sapiensβ2(1-217) I142Y, H. sapiens β1 H-NOX H105G, H. sapiens β1 H-NOX H105F,H. sapiens β1 H-NOX C78S, H. sapiens β1 H-NOX C78E, wild-type R.norvegicus β1 H-NOX, R. norvegicus β1(1-385), R. norvegicus β1(1-385)I145Y, R. norvegicus β1(1-385) I145H, R. norvegicus β1(1-194), R.norvegicus β1(1-194) I145Y, R. norvegicus β1(1-194) L9W-I145Y, R.norvegicus β2(1-217), R. norvegicus β2(1-217) I142Y, R. norvegicus β1H-NOX H105G, R. norvegicus β1 H-NOX H105F, R. norvegicus sGC β1 H-NOXC78S, R. norvegicus sGC β1 H-NOX C78E, C. botulinum H-NOX(1-175), C.botulinum H-NOX(1-186), wild-type C. acetobutylicum H-NOX, C.acetobutylicum H-NOX(1-197), C. acetobutylicum H-NOX(1-183), wild-typeC. elegans GCY-35 H-NOX, C. elegans H-NOX GCY-35(1-252), wild-type D.melangaster β1 H-NOX, wild-type D. melangaster CG14885-PA, wild-type D.melangaster CG 14886, wild-type D. melangaster CG4154; wild-type N.punctiforme H-NOX, wild-type C. crescentus H-NOX, wild-type S.oneidensis H-NOX, wild-type M. musculus H-NOX, wild-type C. familiarisH-NOX, wild-type B. Taurus H-NOX, wild-type R. norvegicus; wild-type X.laevis H-NOX, wild-type O. latipes H-NOX, wild-type O. curivatus H-NOX,wild-type F. rubripes H-NOX, wild-type A. gambiae H-NOX, wild-type M.sexta H-NOX; wild-type C. elegans gcy-31, C. elegans gcy-32, wild-typeC. elegans gcy-33, wild-type C. elegans gcy-34, wild-type C. elegansgcy-35, wild-type C. elegans gcy-36, wild-type C. elegans gcy-37;wild-type V. cholera H-NOX, wild-type V. fischerii H-NOX, and wild-typeN. punctiforme H-NOX. In particular embodiments of the pharmaceuticalcompositions, the H-NOX protein is a selected from the group consistingof wild-type R. norvegicus sGC, wild-type R. norvegicus β1(1-385), R.norvegicus β1(1-217), R. norvegicus β1(1-194), wild-type T.tengcongensis H-NOX, T. tengcongensis H-NOX Y140L, T. tengcongensisH-NOX Y140F, wild-type L. pneumophilia 1 H-NOX, wild-type L.pneumophilia 2 H-NOX, and L. pneumophilia 2 H-NOX F142Y. In someembodiments of the pharmaceutical compositions, the pharmaceuticalcomposition includes one or more liposomes or nanoparticles that includeor encapsulate the H-NOX protein.

In some embodiments of the pharmaceutical compositions, the H-NOXprotein is not T. tengcongensis H-NOX Y40L, wild-type T. tengcongensisH-NOX, wild-type R. norvegicus sGC, or L. pneumophilia 2 H-NOX F142Y. Insome embodiments of the pharmaceutical compositions, the H-NOX proteinis not T. tengcongensis H-NOX F78Y/Y140L. In some embodiments of thepharmaceutical compositions, the H-NOX protein is not wild-type L.pneumophilia 2 H-NOX, wild-type H. sapiens β1 H-NOX, R. norvegicus sGCβ1 H-NOX (1-385), wild-type R. norvegicus β1 H-NOX, wild-type D.melangaster β1 H-NOX, wild-type D. melangaster CG14885-PA H-NOX,wild-type C. elegans GCY-35 H-NOX, wild-type N. punctiforme H-NOX,wild-type C. crescentus H-NOX, wild-type S. oneidensis H-NOX, orwild-type C. acetobutylicum H-NOX. In some embodiments of thepharmaceutical compositions, the H-NOX protein is not T. tengcongensisH-NOX W9F, T. tengcongensis H-NOX Y140F, R. norvegicus sGC β1 H-NOXH105G, R. norvegicus sGC β1 H-NOX H105F, R. norvegicus sGC β1 H-NOXI145Y, R. norvegicus sGC β1 H-NOX C78S, or R. norvegicus sGC β1 H-NOXC78E. In some embodiments of the pharmaceutical compositions, the H-NOXprotein is not R. norvegicus β2(1-217), R. norvegicus β1(1-194), R.norvegicus β1(1-385), or R. norvegicus β1(1-385) I145Y. In someembodiments of the pharmaceutical compositions, the H-NOX protein is notT. tengcongensis H-NOX W9F, T. tengcongensis H-NOX Y140F, or H. sapiensβ1 H-NOX (1-385) I145Y. In some embodiments of the pharmaceuticalcompositions, the H-NOX protein is not T. tengcongensis H-NOX Y140H, H.sapiens β1 I140Y, or H. sapiens β1 I145Y. In some embodiments of thepharmaceutical compositions, the H-NOX protein is not T. tengcongensisH-NOX Y40L, T. tengcongensis H-NOX F78Y/Y140L, T. tengcongensis H-NOXW9F, T. tengcongensis H-NOX Y140F, wild-type T. tengcongensis H-NOX, L.pneumophilia 2 H-NOX F142Y, wild-type L. pneumophilia 2 H-NOX, H.sapiens β1 H-NOX I140Y, H. sapiens B1 I145Y, wild-type H. sapiens β1H-NOX, R. norvegicus sGC β1 H-NOX (1-385), R. norvegicus sGC β1 H-NOX(1-385) I145Y, R. norvegicus sGC β1 H-NOX H105G, R. norvegicus sGC β1H-NOX H105F, R. norvegicus sGC β1 H-NOX I145Y, wild-type R. norvegicusβ1 H-NOX, wild-type D. melangaster β1 H-NOX, wild-type D. melangasterCG14885-PA H-NOX, wild-type C. elegans GCY-35 H-NOX, wild-type N.punctiforme H-NOX, wild-type C. crescentus H-NOX, wild-type S.oneidensis H-NOX, or wild-type C. acetobutylicum H-NOX. In someembodiments of the pharmaceutical compositions, the H-NOX protein is notany of the following H-NOX proteins that are listed by their gene name,followed by their species abbreviation and Genbank Identifiers (such asthe following protein sequences available as of May 21, 2006; May 22,2006; May 21, 2007; or May 22, 2007): Npun5905_Npu_(—)23129606,alr2278_Ana_(—)17229770, SO2144_Sone_(—)24373702,Mdeg1343_Mde_(—)23027521, VCA0720_Vch_(—)15601476,CC2992_Ccr_(—)16127222, Rsph2043_Rhsp_(—)22958463 (gi:46192757),Mmc10739_Mcsp_(—)22999020, Tar4_Tte_(—)20807169,Ddes2822_Dde_(—)23475919, CAC3243_Cac_(—)15896488,gcy-31_Ce_(—)17568389, CG14885_Dm_(—)24647455, GUCY1B3_Hs_(—)4504215,HpGCS-beta1_Hpul_(—)14245738, Gycbeta100B_DM_(—)24651577,CG4154_Dm_(—)24646993 (gi:NP_(—)650424.2, gi:62484298),gcy-32_Ce_(—)13539160,gcy-36_Ce_(—)17568391 (gi:32566352, gi:86564713),gcy-35_Ce-17507861 (gi:71990146), gcy-37_Ce_(—)17540904 (gi:71985505),GCY1α3_Hs_(—)20535603, GCY1α2-Hs_(—)899477, or GYCα-99B_Dm_(—)729270(gi:68067738) (Lakshminarayan et al. (2003). “Ancient conserved domainsshared by animal soluble guanylyl cyclases and bacterial signalingproteins,” BMG Genomics 4:5-13). The species abbreviations used in thesenames include Ana—Anabaena Sp; Ccr—Caulobacter crescentus;Cac—Clostridium acetobutylicum; Dde—Desulfovibrio desulfuricans;Mcsp—Magnetococcus sp.; Mde—Microbulbifer degradans; Npu—Nostocpunctiforme; Rhsp—Rhodobacter sphaeroides; Sone—Shewanella oneidensis;Tte—Thermoanaerobacter tengcongensis; Vch—Vibrio cholerae;Ce—Caenorhabditis elegans; Dm—Drosophila melanogaster;Hpul—Hemicentrotus pukherrimus; Hs—Homo sapiens. In some embodiments ofthe pharmaceutical compositions, the H-NOX protein is not any of thefollowing H-NOX proteins that are listed by their organism name and Pfamdatabase accession number (such as the following protein sequencesavailable as of May 21, 2006; May 22, 2006; May 17, 2007; May 21, 2007;or May 22, 2007): Caenorhabditis briggsae Q622M5CAEBR, Caenorhabditisbriggsae Q61P44_CAEBR, Caenorhabditis briggsae Q61R54_CAEBR,Caenorhabditis briggsae Q61V90_CAEBR, Caenorhabditis briggsaeQ61A94_CAEBR, Caenorhabditis briggsae Q60TP4_CAEBR, Caenorhabditisbriggsae Q60M10_CAEBR, Caenorhabditis elegans GCY37_CAEEL,Caenorhabditis elegans GCY31_CAEEL, Caenorhabditis elegans GCY36_CAEEL,Caenorhabditis elegans GCY32_CAEEL, Caenorhabditis elegans GCY35_CAEEL,Caenorhabditis elegans GCY34_CAEEL, Caenorhabditis elegans GCY33_CAEEL,Oryzias curvinotus Q7T040_ORYCU, Oryzias curvinotus Q75WF0_ORYCU,Oryzias latipes P79998_ORYLA, Oryzias latipes Q7ZSZ5_ORYLA, Tetraodonnigroviridis Q4SW38_TETNG, Tetraodon nigroviridis Q4RZ94_TETNG,Tetraodon nigroviridis Q4S6K5_TETNG, Fugu rubripes Q90VY5_FUGRU, Xenopuslaevis Q6INK9_XENLA, Homo sapiens Q5T8J7_HUMAN, Homo sapiensGCYA2_HUMAN, Homo sapiens GCYB2_HUMAN, Homo sapiens GCYB1_HUMAN, Gorillagorilla Q9N193_(—)9PRIM, Pongo pygmaeus Q5RAN8_PONPY, Pan troglodytesQ9N192_PANTR, Macaca mulatta Q9N 194_MACMU, Hylobates lar Q9N191_HYLLA,Mus musculus Q8BXH3_MOUSE, Mus musculus GCYB1 MOUSE, Mus musculus Q3UTI4MOUSE, Mus musculus Q3UH83_MOUSE, Mus musculus Q6XE41_MOUSE, Musmusculus Q80YP4_MOUSE, Rattus norvegicus Q80WX7_RAT, Rattus norvegicusQ80WX8_RAT, Rattus norvegicus Q920Q1_RAT, Rattus norvegicus Q54A43_RAT,Rattus norvegicus Q80WY0_RAT, Rattus norvegicus Q80WY4_RAT, Rattusnorvegicus Q8CH85_RAT, Rattus norvegicus Q80WY5_RAT, Rattus norvegicusGCYB1_RAT, Rattus norvegicus Q8CH90_RAT, Rattus norvegicus Q91XJ7_RAT,Rattus norvegicus Q80WX9_RAT, Rattus norvegicus GCYB2_RAT, Rattusnorvegicus GCYA2_RAT, Canis familiaris Q4ZHR9_CANFA, Bos taurusGCYB1_BOVIN, Sus scrofa Q4ZHR7_PIG, Gryllus bimaculatus Q59HN5_GRYBI,Manduca sexta O77106 MANSE, Manduca sexta O76340_MANSE, Apis melliferaQ5UAF0_APIME, Apis mellifera Q5FAN0_APIME, Apis mellifera Q6L5L6_APIME,Anopheles gambiae str PEST Q7PYK9_ANOGA, Anopheles gambiae str PESTQ7Q9W6_ANOGA, Anopheles gambiae str PEST Q7QF31_ANOGA, Anopheles gambiaestr PEST Q7PS01_ANOGA, Anopheles gambiae str PEST Q7PFY2_ANOGA,Anopheles gambiae Q7KQ93_ANOGA, Drosophila melanogaster Q24086_DROME,Drosophila melanogaster GCYH_DROME, Drosophila melanogaster GCY8E_DROME,Drosophila melanogaster GCYDA_DROME, Drosophila melanogasterGCYDB_DROME, Drosophila melanogaster Q9VA09_DROME, Drosophilapseudoobscura Q29CE1_DROPS, Drosophila pseudoobscura Q296C7_DROPS,Drosophila pseudoobscura Q296C8_DROPS, Drosophila pseudoobscuraQ29BU7_DROPS, Aplysia californica Q7YWK7_APLCA, Hemicentrotuspulcherrimus Q95NK5_HEMPU, Chlamydomonas reinhardtii, Q5YLC2_CHLRE,Anabaena sp Q8YUQ7_ANASP, Flavobacteria bacterium BBFL7 Q26GR8_(—)9BACT,Psychroflexus torquis ATCC 700755 Q1VQE5_(—)9FLAO, marine gammaproteobacterium HTCC2207 Q1YPJ5_(—)9GAMM, marine gamma proteobacteriumHTCC2207 Q 1YTK4_(—)9GAMM, Caulobacter crescentus Q9A451_CAUCR,Acidiphilium cryptum JF-5 Q2DG60_ACICY, Rhodobacter sphaeroidesQ3J0U9_RHOS4, Silicibacter pomeroyi Q5LPV1_SILPO, Paracoccusdenitrificans PD1222, Q3PC67_PARDE, Silicibacter sp TM1040Q3QNY2_(—)9RHOB, Jannaschia sp Q28ML8_JANSC, Magnetococcus sp MC-1Q3XT27_(—)9PROT, Legionella pneumophila Q5WXP0_LEGPL, Legionellapneumophila Q5WTZ5_LEGPL, Legionella pneumophila Q5X268_LEGPA,Legionella pneumophila Q5X2R2_LEGPA, Legionella pneumophila subsppneumophila Q5ZWM9_LEGPH, Legionella pneumophila subsp pneumophilaQ5ZSQ8_LEGPH, Colwellia psychrerythraea Q47Y43_COLP3, Pseudoalteromonasatlantica T6c Q3CSZ5_ALTAT, Shewanella oneidensis Q8EF49_SHEON,Saccharophagus degradans Q21 E20_SACD2, Saccharophagus degradansQ21ER7_SACD2, Vibrio angustum S14 Q1ZWE5_(—)9VIBR, Vibrio vulnificusQ8DAE2_VIBVU, Vibrio alginolyticus 12G01 Q1VCP6_VIBAL, Vibrio sp DAT722Q2FA22_(—)9VIBR, Vibrio parahaemolyticus Q87NJ1_VIBPA, Vibrio fischeriQ5E1F5_VIBF1, Vibrio vulnificus Q7MJS8_VIBVY, Photobacterium sp SKA34Q2C6Z5_(—)9GAMM, Hahella chejuensis Q2SFY7_HAHCH, Oceanospirillum spMED92 Q2BKV0_(—)9GAMM, Oceanobacter sp RED65 Q1NO35_(—)9GAMM,Desulfovibrio desulfuricans Q310U7_DESDG, Halothermothrix orenii H 168Q2AIW5_(—)9FIRM, Thermoanaerobacter tengcongensis Q8RBX6_THETN,Caldicellulosiruptor saccharolyticus DSM 8903 Q2ZH17_CALSA, Clostridiumacetobutylicum Q97E73_CLOAB, Alkaliphilus metalliredigenes QYMFQ3C763_(—)9CLOT, Clostridium tetani Q899J9_CLOTE, and Clostridiumbeijerincki NCIMB 8052 Q2WVN0_CLOBE. In some embodiments of thepharmaceutical compositions, the H-NOX protein does not have a mutationin the Y-S-R motif, which includes Tyr135, Ser137, and Arg139 of humanH-NOX.

Unless otherwise explicitly noted or dictated by context, all wild-typeand mutant H-NOX proteins described herein may be used in any of thepharmaceutical compositions described herein. The H-NOX protein may ormay not have heme and/or NO bound and may or may not be covalently boundto another molecule or moiety, such as polyethylene glycol. In someembodiments, the H-NOX protein is a fusion protein that includes anH-NOX domain and part or all of another protein, such as albumin (e.g.,human serum albumin).

In one aspect, the invention provides methods of delivering NO to anindividual (e.g., a mammal, such as a primate (e.g., a human, a monkey,a gorilla, an ape, a lemur, etc), a bovine, an equine, a porcine, acanine, or a feline) using an H-NOX protein. In some embodiments, theindividual is suffering from or at risk for a cardiovascular condition,hypertension, a condition exacerbated by hypertension, avasoconstrictive condition, stroke, or a functional NO deficiency. Inparticular embodiments, the condition exacerbated by hypertension isheart failure, renal failure, or a stroke.

Accordingly, in some embodiments, the invention provides a method ofdelivering NO to an individual (e.g., a human) by administering to anindividual in need thereof an H-NOX protein in an amount sufficient todeliver an effective amount of NO to the individual. In someembodiments, the k_(off), k₁, or k₂ for NO of the H-NOX protein isbetween about 1×10⁻⁴ s⁻¹ to about 10 s⁻¹ at 37° C., and the O₂dissociation constant of the H-NOX protein is at least about 1 ηM at 37°C. In some embodiments, the NO dissociation constant of the H-NOXprotein is within 2 orders of magnitude of that of hemoglobin, and theNO reactivity of the H-NOX protein is at least 10-fold lower than thatof hemoglobin.

In some embodiments of the methods, NO is bound to the H-NOX proteinprior to the administration of the H-NOX protein to the individual. Insome embodiments of the methods, NO is not bound to the H-NOX proteinprior to the administration of the H-NOX protein to the individual, andthe H-NOX protein transports NO from one location in the individual toanother location in the individual. In some embodiments of the methods,the H-NOX protein is administered orally, rectally, or to the blood ofthe individual. In particular embodiments of the methods, the H-NOXprotein is administered to the blood of the individual. In someembodiments of the methods, the H-NOX protein is administered to theindividual at least twice.

In some embodiments of the methods, the NO dissociation constant of theH-NOX protein is within 2 orders of magnitude of that of Homo sapienshemoglobin alpha, such as an NO dissociation constant between 0.1 to10-fold or between 0.5 to 2-fold of that of Homo sapiens hemoglobinalpha. In some embodiments of the methods, the NO reactivity of theH-NOX protein is at least 10-fold lower than that of Homo sapienshemoglobin alpha, such as at least 100-fold or 1,000-fold lower thanthat of Homo sapiens hemoglobin alpha. In some embodiments of themethods, the H-NOX protein is a wild-type protein. In some embodimentsof the methods, the H-NOX protein is a mutant protein as describedherein. In various embodiments of the methods, the H-NOX protein has atleast one mutation that alters the NO dissociation constant, the k_(off)for NO, the k₁ for NO, the k₂ for NO, the O₂ dissociation constant, theNO stability, the NO reactivity the rate of heme autoxidation, or anycombination of two or more of the foregoing compared to that of acorresponding wild-type protein. In some embodiments of the methods, theH-NOX protein is a selected from the group consisting of wild-type T.tengcongensis H-NOX, T. tengcongensis H-NOX I5A, T. tengcongensis H-NOXI5L, T. tengcongensis H-NOX I5L-P115A, T. tengcongensis H-NOX W9F, T.tengcongensis H-NOX W9F-Y140L, T. tengcongensis H-NOX W9F-Y140HT.tengcongensis H-NOX W9F-N74A, T. tengcongensis H-NOX W9Y, T.tengcongensis H-NOX W9N, T. tengcongensis H-NOX W9H, T. tengcongensisH-NOX N74E, T. tengcongensis H-NOX N74A, T. tengcongensis H-NOX N74H, T.tengcongensis H-NOX N74A-Y140H, T. tengcongensis H-NOX F78Y-Y140F, T.tengcongensis H-NOX F78Y/Y140L, T. tengcongensis H-NOX P115A, T.tengcongensis H-NOX R135Q, T. tengcongensis H-NOX Y140F, T.tengcongensis H-NOX Y40L, T. tengcongensis H-NOX Y140H, T. tengcongensisH-NOX Y140A, T. tengcongensis I75F-His6, T. tengcongensis I75F, T.tengcongensis L144F-His6, T. tengcongensis L144F, L. pneumophilia 2H-NOX F142Y, wild-type L. pneumophilia 1 H-NOX, wild-type L.pneumophilia 2 H-NOX, L. pneumophilia 2 F9W-F142Y, wild-type D.desulfuricans H-NOX, D. desulfuricans H-NOX(728-899), D. desulfuricansH-NOX Y139L, wild-type H. sapiens β1 H-NOX, H. sapiens β1 I140Y, H.sapiens β1 I145Y, H. sapiens β1(1-385), H. sapiens β1(1-385) I145Y, H.sapiens β1(1-385) I145H, H. sapiens β1(1-194), H. sapiens β1(1-194)I145Y, H. sapiens β1(1-194) L9W-I145Y, H. sapiens β2(1-217), H. sapiensβ2(1-217) I142Y, H. sapiens β1 H-NOX H105G, H. sapiens β1 H-NOX H105F,H. sapiens β1 H-NOX C78S, H. sapiens β1 H-NOX C78E, wild-type R.norvegicus β1 H-NOX, R. norvegicus β1(1-385), R. norvegicus β1(1-385)I145Y, R. norvegicus β1(1-385) I245H, R. norvegicus β1(1-194), R.norvegicus β1(1-194) I145Y, R. norvegicus β1(1-194) L9W-I145Y, R.norvegicus β2(1-217), R. norvegicus β2(1-217) I142Y, R. norvegicus β1H-NOX H105G, R. norvegicus β1 H-NOX H105F, R. norvegicus sGC β1 H-NOXC78S, R. norvegicus sGC β1 H-NOX C78E, C. botulinum H-NOX(1-175), C.botulinum H-NOX(1-186), wild-type C. acetobutylicum H-NOX, C.acetobutylicum H-NOX(1-197), C. acetobutylicum H-NOX(1-183), wild-typeC. elegans GCY-35 H-NOX, C. elegans H-NOX GCY-35(1-252), wild-type D.melangaster β1 H-NOX, wild-type D. melangaster CG14885-PA, wild-type D.melangaster CG14886, wild-type D. melangaster CG4154; wild-type N.punctiforme H-NOX, wild-type C. crescentus H-NOX, wild-type S.oneidensis H-NOX, wild-type M. musculus H-NOX, wild-type C. familiarisH-NOX, wild-type B. Taurus H-NOX, wild-type R. norvegicus; wild-type X.laevis H-NOX, wild-type O. latipes H-NOX, wild-type O. curivatus H-NOX,wild-type F. rubripes H-NOX, wild-type A. gambiae H-NOX, wild-type M.sexta H-NOX; wild-type C. elegans gcy-31, C. elegans gcy-32, wild-typeC. elegans gcy-33, wild-type C. elegans gcy-34, wild-type C. elegansgcy-35, wild-type C. elegans gcy-36, wild-type C. elegans gcy-37;wild-type V. cholera H-NOX, wild-type V. fischerii H-NOX, and wild-typeN. punctiforme H-NOX. In some embodiments of the methods, the H-NOXprotein is a selected from the group consisting of wild-type R.norvegicus sGC, wild-type R. norvegicus β1(1-385), R. norvegicusβ1(1-217), R. norvegicus β1(1-194), wild-type T. tengcongensis H-NOX, T.tengcongensis H-NOX Y140L, T. tengcongensis H-NOX Y140F, wild-type L.pneumophilia 1 H-NOX, wild-type L. pneumophilia 2 H-NOX, and L.pneumophilia 2 H-NOX F142Y. In some embodiments of the methods, one ormore liposomes or nanoparticles that include or encapsulate the H-NOXprotein.

In some embodiments of the methods, the H-NOX protein is not T.tengcongensis H-NOX Y40L, wild-type T. tengcongensis H-NOX, wild-type R.norvegicus sGC, or L. pneumophilia 2 H-NOX F142Y. In some embodiments ofthe methods, the H-NOX protein is not T. tengcongensis H-NOX F78Y/Y140L.In some embodiments of the methods, the H-NOX protein is not wild-typeL. pneumophilia 2 H-NOX, wild-type H. sapiens β1 H-NOX, R. norvegicussGC β1 H-NOX (1-385), wild-type R. norvegicus β1 H-NOX, wild-type D.melangaster β1 H-NOX, wild-type D. melangaster CG14885-PA H-NOX,wild-type C. elegans GCY-35 H-NOX, wild-type N. punctiforme H-NOX,wild-type C. crescentus H-NOX, wild-type S. oneidensis H-NOX, orwild-type C. acetobutylicum H-NOX. In some embodiments of the methods,the H-NOX protein is not T. tengcongensis H-NOX W9F, T. tengcongensisH-NOX Y140F, R. norvegicus sGC β1 H-NOX H105G, R. norvegicus sGC β1H-NOX H105F, R. norvegicus sGC β1 H-NOX I145Y, R. norvegicus sGC β1H-NOX C78S, or R. norvegicus sGC β1 H-NOX C78E. In some embodiments ofthe methods, the H-NOX protein is not R. norvegicus β2(1-217), R.norvegicus β1(1-194), R. norvegicus β1(1-385), or R. norvegicusβ1(1-385) 1145Y. In some embodiments of the methods, the H-NOX proteinis not T. tengcongensis H-NOX W9F, T. tengcongensis H-NOX Y140F, or H.sapiens β1 H-NOX (1-385) I145Y. In some embodiments of the methods, theH-NOX protein is not T. tengcongensis H-NOX Y140H, H. sapiens β1 I140Y,or H. sapiens β1 I145Y. In some embodiments of the methods, the H-NOXprotein is not T. tengcongensis H-NOX Y40L, T. tengcongensis H-NOXF78Y/Y140L, T. tengcongensis H-NOX W9F, T. tengcongensis H-NOX Y140F,wild-type T. tengcongensis H-NOX, L. pneumophilia 2 H-NOX F142Y,wild-type L. pneumophilia 2 H-NOX, H. sapiens β1 H-NOX I140Y, H. sapiensB1 I145Y, wild-type H. sapiens β1 H-NOX, R. norvegicus sGC β1 H-NOX(1-385), R. norvegicus sGC β1 H-NOX (1-385) I145Y, R. norvegicus sGC β1H-NOX H105G, R. norvegicus sGC β1 H-NOX H105F, R. norvegicus sGC β1H-NOX I145Y, wild-type R. norvegicus β1 H-NOX, wild-type D. melangasterβ1 H-NOX, wild-type D. melangaster CG14885-PA H-NOX, wild-type C.elegans GCY-35 H-NOX, wild-type N. punctiforme H-NOX, wild-type C.crescentus H-NOX, wild-type S. oneidensis H-NOX, or wild-type C.acetobutylicum H-NOX. In some embodiments of the methods, the H-NOXprotein is not any of the following H-NOX proteins that are listed bytheir gene name, followed by their species abbreviation and GenbankIdentifiers (such as the following protein sequences available as of May21, 2006; May 22, 2006; May 21, 2007; or May 22, 2007):Npun5905_Npu_(—)23129606, alr2278_Ana_(—)17229770,SO2144_Sone_(—)24373702, Mdeg1343_Mde_(—)23027521,VCA0720_Vch_(—)15601476, CC2992_Ccr_(—)1 6127222,Rsph2043_Rhsp_(—)22958463 (gi:46192757), Mmc10739_Mcsp_(—)22999020,Tar4_Tte_(—)20807169, Ddes2822_Dde_(—)23475919, CAC3243_Cac_(—)15896488,gcy-31_Ce_(—)17568389, CG14885_Dm_(—)24647455, GUCY1B3_Hs_(—)4504215,HpGCS-beta1_Hpul_l 4245738, Gycbeta 100B_Dm_(—)24651577,CG4154_Dm_(—)24646993 (gi:NP_(—)650424.2, gi:62484298),gcy-32_Ce_(—)13539160,gcy-36_Ce_(—)17568391 (gi:32566352, gi:86564713),gcy-35_Ce-17507861 (gi:71990146), gcy-37_Ce_(—)17540904 (gi:71985505),GCY1α3_Hs_(—)20535603, GCY1α2-Hs_(—)899477, or GYCα-99B_Dm_(—)729270(gi:68067738) (Lakshminarayan et al. (2003). “Ancient conserved domainsshared by animal soluble guanylyl cyclases and bacterial signalingproteins,” BMG Genomics 4:5-13). The species abbreviations used in thesenames include Ana—Anabaena Sp; Ccr—Caulobacter crescentus;Cac—Clostridium acetobutylicum; Dde—Desulfovibrio desulfuricans;Mcsp—Magnetococcus sp.; Mde—Microbulbifer degradans; Npu—Nostocpunctiforme; Rhsp—Rhodobacter sphaeroides; Sone—Shewanella oneidensis;Tte—Thermoanaerobacter tengcongensis; Vch—Vibrio cholerae;Ce—Caenorhabditis elegans; Dm—Drosophila melanogaster;Hpul—Hemicentrotus pulcherrimus; Hs—Homo sapiens. In some embodiments ofthe methods, the H-NOX protein is not any of the following H-NOXproteins that are listed by their organism name and Pfam databaseaccession number (such as the following protein sequences available asof May 21, 2006; May 22, 2006; May 17, 2007; May 21, 2007; or May 22,2007): Caenorhabditis briggsae Q622M5_CAEBR, Caenorhabditis briggsaeQ61P44_CAEBR, Caenorhabditis briggsae Q61R54_CAEBR, Caenorhabditisbriggsae Q61V90_CAEBR, Caenorhabditis briggsae Q61A94_CAEBR,Caenorhabditis briggsae Q60TP4_CAEBR, Caenorhabditis briggsaeQ60M10_CAEBR, Caenorhabditis elegans GCY37_CAEEL, Caenorhabditis elegansGCY31_CAEEL, Caenorhabditis elegans GCY36_CAEEL, Caenorhabditis elegansGCY32_CAEEL, Caenorhabditis elegans GCY35_CAEEL, Caenorhabditis elegansGCY34_CAEEL, Caenorhabditis elegans GCY33_CAEEL, Oryzias curvinotusQ7T040_ORYCU, Oryzias curvinotus Q75WF0_ORYCU, Oryzias latipes P79998ORYLA, Oryzias latipes Q7ZSZ5_ORYLA, Tetraodon nigroviridisQ4SW38_TETNG, Tetraodon nigroviridis Q4RZ94_TETNG, Tetraodonnigroviridis Q4S6K5_TETNG, Fugu rubripes Q90VY5_FUGRU, Xenopus laevisQ6INK9_XENLA, Homo sapiens Q5T8J7_HUMAN, Homo sapiens GCYA2_HUMAN, Homosapiens GCYB2_HUMAN, Homo sapiens GCYB1_HUMAN, Gorilla gorillaQ9N193_(—)9PRIM, Pongo pygmaeus Q5RAN8_PONPY, Pan troglodytesQ9N192_PANTR, Macaca mulatta Q9N194_MACMU, Hylobates lar Q9N191_HYLLA,Mus musculus Q8BXH3_MOUSE, Mus musculus GCYB1_MOUSE, Mus musculusQ3UTI4_MOUSE, Mus musculus Q3UH83_MOUSE, Mus musculus Q6XE41_MOUSE, Musmusculus Q80YP4_MOUSE, Rattus norvegicus Q80WX7_RAT, Rattus norvegicusQ80WX8_RAT, Rattus norvegicus Q920Q1_RAT, Rattus norvegicus Q54A43 RAT,Rattus norvegicus Q80WY0_RAT, Rattus norvegicus Q80WY4_RAT, Rattusnorvegicus Q8CH85_RAT, Rattus norvegicus Q80WY5_RAT, Rattus norvegicusGCYB1_RAT, Rattus norvegicus Q8CH90_RAT, Rattus norvegicus Q91XJ7_RAT,Rattus norvegicus Q80WX9_RAT, Rattus norvegicus GCYB2_RAT, Rattusnorvegicus GCYA2_RAT, Canis familiaris Q4ZHR9_CANFA, Bos taurus GCYB1BOVIN, Sus scrofa Q4ZHR7_PIG, Gtyllus bimaculatus Q59HN5_GRYBI, Manducasexta O77106_MANSE, Manduca sexta O76340_MANSE, Apis melliferaQ5UAF0_APIME, Apis mellifera Q5FAN0_APIME, Apis mellifera Q6L5L6_APIME,Anopheles gambiae str PEST Q7PYK9_ANOGA, Anopheles gambiae str PESTQ7Q9W6_ANOGA, Anopheles gambiae str PEST Q7QF31_ANOGA, Anopheles gambiaestr PEST Q7PS01_ANOGA, Anopheles gambiae str PEST Q7PFY2_ANOGA,Anopheles gambiae Q7KQ93_ANOGA, Drosophila melanogaster Q24086_DROME,Drosophila melanogaster GCYH_DROME, Drosophila melanogaster GCY8E_DROME,Drosophila melanogaster GCYDA_DROME, Drosophila melanogasterGCYDA_DROME, Drosophila melanogaster Q9VA09_DROME, Drosophilapseudoobscura Q29CE1_DROPS, Drosophila pseudoobscura Q296C7_DROPS,Drosophila pseudoobscura Q296C8_DROPS, Drosophila pseudoobscuraQ29BU7_DROPS, Aplysia californica Q7YWK7_APLCA, Hemicentrotuspulcherrimus Q95NK5_HEMPU, Chlamydomonas reinhardtii, Q5YLC2_CHLRE,Anabaena sp Q8YUQ7_ANASP, Flavobacteria bacterium BBFL7 Q26GR8_(—)9BACT,Psychroflexus torquis ATCC 700755 Q1VQE5_(—)9FLAO, marine gammaproteobacterium HTCC2207 Q1YPJ5_(—)9GAMM, marine gamma proteobacteriumHTCC2207 Q1YTK4_(—)9GAMM, Caulobacter crescentus Q9A451_CAUCR,Acidiphilium cryptum JF-5 Q2DG60_ACICY, Rhodobacter sphaeroidesQ3J0U9_RHOS4, Silicibacter pomeroyi Q5LPV1_SILPO, Paracoccusdenitrificans PD1222, Q3PC67_PARDE, Silicibacter sp TM1040Q3QNY2_(—)9RHOB, Jannaschia sp Q28ML8_JANSC, Magnetococcus sp MC-1Q3XT27_(—)9PROT, Legionella pneumophila Q5WXP0_LEGPL, Legionellapneumophila Q5WTZ5_LEGPL, Legionella pneumophila Q5X268_LEGPA,Legionella pneumophila Q5X2R2_LEGPA, Legionella pneumophila subsppneumophila Q5ZWM9_LEGPH, Legionella pneumophila subsp pneumophilaQ5ZSQ8_LEGPH, Colwellia psychrerythraea Q47Y43_COLP3, Pseudoalteromonasatlantica T6c Q3CSZ5_ALTAT, Shewanella oneidensis Q8EF49_SHEON,Saccharophagus degradans Q21E20_SACD2, Saccharophagus degradansQ21ER7_SACD2, Vibrio angustum S14 Q1ZWE5_(—)9VIBR, Vibrio vulnificusQ8DAE2_VIBVU, Vibrio alginolyticus 12G01 Q1VCP6_VIBAL, Vibrio sp DAT722Q2FA22_(—)9VIBR, Vibrio parahaemolyticus Q87NJ1_VIBPA, Vibrio fischeriQ5E1F5_VIBF1, Vibrio vulnificus Q7MJS8_VIBVY, Photobacterium sp SKA34Q2C6Z5_(—)9GAMM, Hahella chejuensis Q2SFY7_HAHCH, Oceanospirillum spMED92 Q2BKV0_(—)9GAMM, Oceanobacter sp RED65 QIN035_(—)9GAMM,Desulfovibrio desulfuricans Q310U7_DESDG, Halothermothrix orenii H 168Q2AIW5_(—)9FIRM, Thermoanaerobacter tengcongensis Q8RBX6_THETN,Caldicellulosiruptor saccharolyticus DSM 8903 Q2ZH17CALSA, Clostridiumacetobutylicum Q97E73_CLOAB, Alkaliphilus metalliredigenes QYMFQ3C763_(—)9CLOT, Clostridium tetani Q899J9_CLOTE, and Clostridiumbeijerincki NCIMB 8052 Q2WVN0_CLOBE. In some embodiments of the methods,the H-NOX protein does not have a mutation in the Y—S—R motif, whichincludes Tyr135, Ser137, and Arg139 of human H-NOX.

Unless otherwise explicitly noted or dictated by context, all wild-typeand mutant proteins and all pharmaceutical compositions described hereinmay be used in any of the methods of delivering NO described herein. TheH-NOX protein may or may not have heme and/or NO bound and may or maynot be covalently bound to another molecule or moiety, such aspolyethylene glycol. In some embodiments, the H-NOX protein is a fusionprotein that includes an H-NOX domain and part or all of anotherprotein, such as albumin (e.g., human serum albumin).

In one aspect, the invention features kits that include one or moreH-NOX proteins. In some embodiments, the invention provides a kit thatincludes an H-NOX protein and instructions for using the kit to deliverNO to an individual. In some embodiments, the k_(off), k₁, or k₂ for NOof the H-NOX protein is between about 1×10−4 s⁻¹ to about 10 s⁻¹ at 37°C., and the O₂ constant of the H-NOX protein is at least about 1 μM at37° C. In some embodiments, the NO dissociation constant of the H-NOXprotein is within 2 orders of magnitude of that of hemoglobin, and theNO reactivity of the H-NOX protein is at least 10-fold lower than thatof hemoglobin. Unless otherwise explicitly noted or dictated by context,all wild-type and mutant proteins and all pharmaceutical compositionsdescribed herein may be used in any of the kits described herein. TheH-NOX protein may or may not have heme and/or NO bound and may or maynot be covalently bound to another molecule or moiety, such aspolyethylene glycol. In some embodiments, the H-NOX protein is a fusionprotein that includes an H-NOX domain and part or all of anotherprotein, such as albumin (e.g., human serum albumin).

In one aspect, the invention features an H-NOX protein (such as any ofthe wild-type or mutant proteins described herein) for use as amedicament. In some embodiments, the invention features an H-NOX proteinfor use in a method of delivering NO to an individual. In someembodiments, the H-NOX protein is used to treat any condition for whichdelivery of NO is beneficial, such as a cardiovascular condition,hypertension, a condition exacerbated by hypertension (e.g., heartfailure, renal failure, or a stroke), a vasoconstrictive condition,stroke, or a functional NO deficiency.

In some embodiments, the invention features the use of an H-NOX protein(such as any of the wild-type or mutant proteins described herein) forthe manufacture of a medicament, such as a medicament for delivering NOto an individual. In some embodiments, the invention features the use ofan H-NOX protein for delivering NO to an individual. In someembodiments, the H-NOX protein is used to treat any condition for whichdelivery of NO is beneficial, such as a cardiovascular condition,hypertension, a condition exacerbated by hypertension (e.g., heartfailure, renal failure, or a stroke), a vasoconstrictive condition,stroke, or a functional NO deficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a picture of the three dimensional structure of distal pocketresidues of NO-binding and O₂-binding H-NOX proteins (above heme). Hemecoordination residues of NO-binding and O₂-binding H-NOX proteins arealso shown (below heme). FIG. 1A is based on the three-dimensionalstructure of T. tengcongensis H-NOX reported by Pellicena, P. et al.(Aug. 31, 2004). “Crystal Structure of An Oxygen-Binding Heme DomainRelated to Soluble Guanylate Cyclases,” Proc Natl. Acad Sci USA101(35):12854-12859.

FIG. 1B is a stereo side view of the three dimensional structure of T.tengcongensis HNOX illustrating structural features of the H-NOX domain.The protein fold is represented by ribbon diagrams. The heme, dioxygenligand, and proximal histidine are shown as ball-and-stick models.α-helices are labeled A-G according to the nomenclature shown in FIG.5B. β-strands are labeled 1-4. FIG. 1B is from Pellicena, P. et al.(Aug. 31, 2004). “Crystal Structure of An Oxygen-Binding Heme DomainRelated to Soluble Guanylate Cyclases,” Proc Natl. Acad Sci USA101(35):12854-12859.

FIGS. 1C-1H are pictures of the three dimensional structure of T.tengcongensis HNOX illustrating exemplary distal pocket residues in T.tengcongensis HNOX. The following residues depicted in FIGS. 1C-1H arethe main residues comprising the H-NOX distal pocket: Thr4, Ile5, Thr8,Trp9, Trp67, Asn74, Ile75, Phe78, Phe82, Tyr140, and Leu144, which arecontained within helices A, D, E, and G. FIGS. 1C-1H were created usingPYMOL (DeLano Scientific, LLP).

FIG. 2 is a sequence alignment of the following H-NOX proteins that bindor are predicted to bind O₂ and NO: Majority (SEQ ID NO:1); Ce. gcy-3l(SEQ ID NO:2); Ce. gcy-33 (SEQ 1D NO:3); Ce. gcy-35 (SEQ ID NO:4); Dm.CG14885 HNOX (SEQ ID NO:5); Dm. CG4154 HNOX (SEQ ID NO:6); Ms. Beta3HNOX (SEQ ID NO:7); Tt HNOX (SEQ ID NO:8); and Ca HNOX (SEQ ID NO:9).These H-NOX proteins are predicted to bind O₂ as well as NO because theyhave a tyrosine at the position corresponding to Y140 of T.tengcongensis H-NOX. The amino acid numbering used in FIG. 2 starts withthe first amino acid in the H-NOX domain or full-length protein asresidue number 1. The alignment was generated using the defaultparameters in the program MegAlign. The abbreviations used in FIG. 2 aredescribed below with respect to FIGS. 4A-4D.

FIG. 3A-3D are a sequence alignment of the following H-NOX proteins thatbind or are predicted to bind NO but not O₂: Majority (SEQ ID NO:10);Dm. sGC beta1 protein (SEQ ID NO:11); sGC beta1 protein (SEQ ID NO:12);hs. sGC beta1 protein (SEQ ID NO:13); hs. beta2 protein (SEQ ID NO:14);Ms. sGC beta1 protein (SEQ ID NO:15); Mm. sGCbeta1 protein (SEQ IDNO:16); Np. beta1 HD-like (SEQ ID NO:17); Tr. sGC beta1 protein (SEQ IDNO:18); Anopheles _(—) gambiae|XP_(—)310919 (SEQ ID NO:19); Apis _(—)mellifera|NP_(—)001011632 (SEQ ID N0:20); Bt. sGC beta1 protein (SEQ IDNO:21); Chlamydomonas _(—) reinhardtii|AAR02 (SEQ ID NO:22); Oryzias_(—) curvinotus|BAC98396 (SEQ ID NO:23); Oryzias _(—) latipes|BAA7669 I(SEQ ID NO:24); Strongylocentrotus _(—) purpuratus|X (SEQ ID NO:25); andSus scrofa beta1|NP_(—)001018042+ (SEQ ID NO:26). The alignment wasgenerated using the default parameters in the program MegAlign. Theabbreviations used in FIGS. 3A-3D are described below with respect toFIG. 4.

FIGS. 4A-4D are a sequence alignment of H-NOX proteins from FIGS. 2 and3A-3D: Majority (SEQ ID NO:27); Dm. sGC beta1 protein (SEQ ID NO:11);sGC beta1 protein (SEQ ID NO:12); hs. sGC beta1 protein (SEQ ID NO:13);hs. beta2 protein (SEQ ID NO:14); Mm. sGC beta1 protein (SEQ ID NO:16);Np. beta1HD-like (SEQ ID NO:17); Tr. sGC beta1 protein (SEQ ID NO:18);Chlamydomonas _(—) reinhardtii|AAR02 (SEQ ID NO:22); Oryzias _(—)curvinotus|BAC98396 (SEQ ID NO:23); Strongylocentrotus _(—) purpuratus|X(SEQ ID NO:25); Sus scrofa beta1|NP_(—)001018042 (SEQ ID NO:26); gcy-31a(SEQ ID NO:2); gcy-33 (SEQ ID NO:3); Ca. HNOX (SEQ ID NO:9); T.beta1HD-like (SEQ ID NO:8); Ms. sGc beta 3 protein (SEQ ID NO:7);CG14885 (SEQ ID NO:5); and Dm. sGC short variant (SEQ ID NO:6). Thealignment was generated using the default parameters in the programMegAlign. For FIGS. 2-4D, “Dm. sGC beta1 protein” denotes Drosophilamelanogaster β1 H-NOX; “sGC beta1 protein” denotes Rattus norvegicus β1H-NOX; “hs. sGC beta1 protein” denotes Homo sapiens β1 H-NOX; “hs. beta2protein” denotes Homo sapiens β2 H-NOX; “Mm. sGC beta1 protein” denotesMus musculus β1 H-NOX; “Np. beta1HD-like” denotes Nostoc punctiformeH-NOX; “Tr. sGC beta1 protein” denotes Talaifugu rubripes β1 H-NOX;“Anopheles _(—) gambiae|XP_(—)310919” denotes Anopheles gambiae β1H-NOX; “Apis _(—) mellifera|NP_(—)001011632” denotes Apis mellifera β1H-NOX; “Bt. sGC beta1 protein” denotes Bos taurus β1 H-NOX;“Chlamydomonas _(—) reinhardtii|AAR02” denotes Chlamydomonas reinhardtiiβ1 H-NOX; “Oryzias _(—) curvinotus|BAC98396 denotes Oryzias curvinotusβ1 H-NOX; “Oryzias _(—) latipes|BAA76691” denotes Oryzias latipes β1H-NOX; “Strongylocentrotus _(—) purpuratus|X” denotes Strongylocentrotuspurpuratus β1 H-NOX; “Sus scrofa beta1|NP_(—)001018042+” denotes Susscrofa β1 H-NOX; “gcy-31a” denotes Caenorhabditis elegans Gcy-31a H-NOX;“gcy-33” denotes Caenorhabditis elegans Gcy-33 H-NOX; “gcy-35” denotesCaenorhabditis elegans Gcy-35 H-NOX; “Ca. HNOX” denotes Clostridiumacetobutiylicum H-NOX; “T. beta1HD-like” denotes Thermoanaerobactertengcongensis H-NOX; “Ms. sGc beta 3 protein” denotes Manduca sexta β3H-NOX; “CG14885” denotes Drosophila melanogaster CG14885 H-NOX; “Dm. sGCshort variant” denotes Drosophila melanogaster Gcy-88-E-S H-NOX, and“Dm. CG4154 HNOX” denotes Drosophila melanogaster CG4154 H-NOX.

FIG. 5A is a sequence alignment of members of the H-NOX family. Thesequence numbering is that of T. tengcongensis H-NOX. Invariant residuesare indicated by a “V”, very highly conserved residues are indicated by“s”. Y 140 of T. tengcongensis H-NOX is indicated by a “H.” Predicteddistal pocket tyrosine residues that may stabilize an Fe^(II)—O₂ complexin other H-NOX proteins are: position 70 for Caenorhabditis elegansGCY-35; position 140 in Drosophila melanogaster CG14885-PA; position 138of Caenorhabditis elegans GCY-35; position 140 of Clostridiumacetobutylicum; numbered according to Thermoanaerobacter tengcongensis.Accession numbers are: Homo sapiens β1 [gi:2746083] (SEQ ID NO:28),Rattus norvegicus β1 [gi:27127318] (SEQ ID NO:29), Drosophilamelangaster β1 [gi:861203] (SEQ ID NO:30), Drosophila melangasterCG14885-PA [gi:23171476] (SEQ ID NO:31), Caenorhabditis elegans GCY-35[gi:52782806] (SEQ ID NO:32), Nostoc punctiforme [gi:23129606] (SEQ IDNO:33), Caulobacter crescentus [gi:16127222] (SEQ ID NO:34), Shewanellaoneidensis [gi:24373702] (SEQ ID NO:35), Legionella pneumophila (ORF 2)[CUCGC_(—)272624] (SEQ ID NO:36), Clostridium acetobutylicum[gi:15896488] (SEQ ID NO:37), and Thermoanaerobacter tengcongensis[gi:20807169] (SEQ ID NO:38). Alignments were generated using theprogram MegAlign, Lasergene, DNA Star, (see, the world-wide web at“dnastar.com/products/megalign.php”). Clustal-W default parameters wereused.

FIG. 5B is a sequence alignment of exemplary H-NOX domains. Thesecondary structure annotations and the numbering on top of thealignment correspond to the H-NOX domain from T. tengcongensis.α-helices are represented by spirals, and β-strands by arrows. Thedistal pocket is defined by α-helices αA, αD, αE, and αG. Pubmed/NCBIaccession numbers are as follows: Ther_tengcongensis gi |120807169| (SEQID NO:39), Clos_acetobutylicum gi |15896488| (SEQ ID NO:40), Clos_tetaniG1:75543266 (SEQ ID NO:41), Desu_desulfuricans gi |23475919| (SEQ IDNO:42), Vibr_vulnificus gi |27361734| (SEQ ID NO:43), Caul_crescentus gi|16127222| (SEQ ID NO:44), Micr_degradans gi |23027521| (SEQ ID NO:45),Vibr_cholerae gi |15601476| (SEQ ID NO:46), Shew oneidensis gi|124373702| (SEQ ID NO:47), Rat_beta1_sGC gi |27127318| (SEQ ID NO:48),Rat_beta2_sGC gi |121956635| (SEQ ID NO:49), Nost_punctiforme gi|23129606| (SEQ ID NO:50), and Nost_sp. gi |17229770| (SEQ ID NO:51).The consensus sequence is shown a the bottom of FIG. 5 B (SEQ ID NO:52).The alignments were generated using the program MULTALIN (Comet, F.(1988) Nucleic Acids Res. 16:10881-10890), and FIG. 5B was preparedusing the program ESPRIPT (Gouet, P. et al. (1999) Bioinformatics 15:305-308.).

FIGS. 6A and 6B are pictures of the three dimensional structure of theheme environment of the T. tengcongensis H-NOX domain. FIGS. 6A and 6Bare from Pellicena, P. et al. (Aug. 31, 2004). “Crystal Structure of AnOxygen-Binding Heme Domain Related to Soluble Guanylate Cyclases,” ProcNatl. Acad Sci USA 101(35):12854-12859.

FIGS. 7A-7F are graphs of the UV-visible spectroscopy of H-NOX proteinsafter anaerobic reduction (Fe^(II) unligated complexes; top line in eachgraph) before and after being exposed to air (Fe^(II)—O₂ complexes;bottom line in each graph) for Tt H-NOX (FIG. 7A), Tt Y140L (FIG. 7B),Tt W9F-Y140L (FIG. 7C), Tt F78Y-Y140L (FIG. 7D), L2 H-NOX and L2 F142Y(FIG. 7E), and β1(1-385) and β1(1-385) I145Y (FIG. 7F). In addition tothe Fe^(II) and Fe^(II)—O₂ complexes of L2 F142Y and β1(1-385) I145Y,the spectrum of wild-type L2 H-NOX and β1-(1-375) H-NOX after reductionand exposure to air are shown in the middle line in FIGS. 7E and 7F,respectively, to demonstrate that these proteins do not bind O₂ beforethe addition of a distal pocket tyrosine. The two or three numberswritten in the upper left corner of each panel represent the wavelengthfor the peak of the lines in the graph. The numbers are writtenvertically in the order in which the corresponding lines appearvertically in the graph. For example, the 430 nm value in FIG. 7Adenotes the peak of the wavelength for the top line in the graph (whichrepresents a Fe^(II) unligated complex), and the 416 nm value in FIG. 7Adenotes the peak of the wavelength for the bottom line in the graph(which represents a Fe^(II)—O₂ complex). A shift in the wavelength inthe presence of air indicates that the protein binds O₂. The formationof a double peak between 500 and 600 nm in the presence of air is alsoindicative of O₂ binding. FIGS. 7A-7F are from Boon, E. M. et al.(2005). “Molecular Basis For NO Selectivity in Soluble GuanylateCyclase,” Nature Chem. Biol. 1:53-59.

FIGS. 8A-8DD contain polynucleotide sequences of exemplary nucleic acidsthat encode H-NOX proteins and the amino acid sequences of thecorresponding H-NOX proteins (SEQ ID NOS:53-162).

DETAILED DESCRIPTION OF THE INVENTION

The present invention is based in part on the surprising discovery thatH-NOX proteins have a much lower NO reactivity than hemoglobin. Thisintrinsic low NO reactivity (and high NO stability) makes wild-type andmutant H-NOX proteins desirable NO carriers because of the lowerprobability of inactivation of H-NOX proteins by NO in the presence ofO₂. Importantly, the presence of a distal pocket tyrosine in some H-NOXproteins (Pellicena, P. et al. (Aug. 31, 2004). “Crystal Structure of AnOxygen-Binding Heme Domain Related to Soluble Guanylate Cyclases,” ProcNatl. Acad Sci USA 101(35):12854-12859) is suggestive of undesirable,high NO reactivity, contraindicating use as an NO carrier. For example,by analogy, a Mycobacterium tuberculosis hemoglobin protein, with astructurally analogous distal pocket tyrosine, reacts extremely rapidlywith NO, and is used by the Mycobacterium to effectively scavenge andavoid defensive NO produced by an infected host (Ouellet, H. et al.(Apr. 30, 2002). “Truncated Hemoglobin HbN Protects Mycobacterium BovisFrom Nitric Oxide,” Proc. Natl. Acad. Sci. USA 99(9):5902-5907).However, we surprisingly discovered that H-NOX proteins actually have amuch lower NO reactivity than that of hemoglobin making their use as NOcarriers possible.

Additionally, it was discovered that the usefulness of H-NOX proteins asNO carriers can be improved by modifying their affinities for NO or O₂to maximize the amount of NO that is bound to the 14-NOX protein and toreduce the amount of H-NOX protein that is oxidized by the reaction ofNO with O₂ bound to the H-NOX protein. In particular, the affinity ofH-NOX proteins for NO or O₂ and the ability of H-NOX proteins todiscriminate between NO and O₂ ligands can be altered by theintroduction of one or more amino acid mutations, allowing H-NOXproteins to be tailored to bind NO or O₂ with desired affinities. Forexample, the dissociation constant or dissociation rate for NO or O₂binding by H-NOX proteins can be altered the introduction of a singleamino acid mutation. Additional mutations can be introduced to furtheralter the affinity for NO and/or O₂. The H-NOX protein family cantherefore be manipulated to exhibit improved or optimal kinetic andthermodynamic properties for NO delivery. For example, mutant H-NOXproteins have been generated with altered dissociation constants and/ordissociation rates for NO binding that improve the usefulness of H-NOXproteins for a variety of clinical and industrial applications. In someembodiments, an H-NOX protein with a low affinity for O₂ (such as an O₂dissociation constant of at least about 1 μM at 37° C.) is used tominimize the amount of O₂ that binds the H-NOX protein, therebyfacilitating the binding of NO to the H-NOX protein and reducing theamount of H-NOX protein that is oxidized due to the reaction of NO withO₂ bound to the heme of the H-NOX protein. This reduction in theoxidation of H-NOX proteins results in less destruction of NO and O₂that can be used by the organs, tissues, and cells of the treatedindividual. The ability to tune H-NOX proteins to bind and deliver NO isa therapeutic avenue that addresses and overcomes the centralshortcomings of current vasodilators. Accordingly, the present inventionprovides proteins, compositions, kits, and methods for the delivery ofNO.

There are numerous benefits of using H-NOX proteins for NO delivery.Organic nitrates are effective for a limited length of time due totolerance. Since H-NOX proteins delivery NO directly to individualswithout requiring the bioconversion of nitrates to NO, the effectivenessof H-NOX proteins as NO carriers is not limited by inhibition of thisbioconversion pathway. Major limitations of hemoglobin-based NO carriersare their high affinity for O₂ and their propensity to be inactivated byNO. As mentioned above, destruction of even low levels of NO byhemoglobin-based carriers can have serious effects on the tonic restingstate of the vasculature and organs and leads to hypertension andgastrointestinal distress. Intra- and inter-molecular cross-linking havebeen used to minimize the toxicity of hemoglobin-based vehicles whenused as oxygen carriers (“Blood Substitutes,” R. Winslow ed. AcademicPress, 2006). While these modifications overcame some of the severetoxicity issues related to extravasation of hemoglobin, the high NOreactivity remained. In contrast, H-NOX proteins have a much lower NOreactivity than hemoglobin. This lower reactivity leads to lessdestruction of NO, O₂, and H-NOX protein since less NO reacts with O₂bound to the H-NOX protein. The ability to select H-NOX proteins withdesired dissociation constants and dissociation rates for NO can alsominimize side-effects by preventing too much NO from being released(causing hypotension) and prevent NO from being released at undesiredsites (e.g., sites that are not vasoconstricted). Engineering H-NOXproteins to bind and deliver NO with minimal NO reactivity provides anew blood gas NO carrier where the H-NOX proteins deliver NO withoutbeing inactivated by NO. These H-NOX proteins, compositions, kits, andmethods are described further herein.

For delivery of NO, engineered H-NOX proteins represent an importantalternative that overcomes the persistent problem of tolerance withcurrent nitrovasodilators. The use of H-NOX proteins as deliveryvehicles for NO provides a new therapeutic venue for treating diseasesexacerbated by chronic hypertension.

H-NOX Proteins

Overview of H-NOX Protein Family

Unless otherwise indicated, any wild-type or mutant H-NOX protein can beused in the compositions, kits, and methods as described herein. As usedherein, an “H-NOX protein” means a protein that has an H-NOX domain(named for Heme-Nitric oxide and OXygen binding domain). An H-NOXprotein may or may not contain one or more other domains in addition tothe H-NOX domain. H-NOX proteins are members of a highly-conserved,well-characterized family of hemoproteins (Iyer, L. M. et al. (Feb. 3,2003). “Ancient Conserved Domains Shared by Animal Soluble GuanylylCyclases And Bacterial Signaling Proteins,” BMC Genomics 4(1):5; Karow,D. S. et al. (Aug. 10, 2004). “Spectroscopic Characterization of theSoluble Guanylate Cyclase-Like Heme Domains From Vibrio Cholerae AndThermoanaerobacter Tengcongensis,” Biochemistry 43(31):10203-10211;Boon, E. M. et al. (2005). “Molecular Basis For NO Selectivity inSoluble Guanylate Cyclase,” Nature Chem. Biol. 1:53-59; Boon, E. M. etal. (October 2005). “Ligand Discrimination in Soluble Guanylate Cyclaseand the H-NOX Family of Heme Sensor Proteins,” Curr. Opin. Chem. Biol.9(5):441-446; Boon, E. M. et al. (2005). “Ligand Specificity of H-NOXDomains: From sGC to Bacterial NO Sensors,” J. Inorg. Biochem.99(4):892-902). H-NOX proteins are also referred to as Pfam 07700proteins or HNOB proteins (Pfam—A database of protein domain familyalignments and Hidden Markov Models, Copyright (C) 1996-2006 The PfamConsortium; GNU LGPL Free Software Foundation, Inc., 59 TemplePlace-Suite 330, Boston, Mass. 02111-1307, USA). In some embodiments, anH-NOX protein has, or is predicted to have, a secondary structure thatincludes six alpha-helices, followed by two beta-strands, followed byone alpha-helix, followed by two beta-strands. An H-NOX protein can bean apoprotein that is capable of binding heme or a holoprotein with hemebound. An H-NOX protein can covalently or non-covalently bind a hemegroup. Some H-NOX proteins bind NO but not O₂, and others bind both NOand O₂. H-NOX domains from facultative aerobes that have been isolatedbind NO but not O₂. H-NOX proteins from obligate aerobic prokaryotes, C.elegans, and D. melanogaster bind NO and O_(2.) Mammals have two H-NOXproteins: β1 and β2. An alignment of mouse, rat, cow, and human H-NOXsequences shows that these species share >99% identity. In someembodiments, the H-NOX domain of an H-NOX protein or the entire H-NOXprotein is at least about any of 10, 15, 20, 25, 30, 40, 50, 60, 70, 80,90, 95, 97, 98, 99, or 99.5% identical to that of the correspondingregion of a naturally-occurring Thermoanaerobacter tengcongensis H-NOXprotein or a naturally-occurring sGC protein (e.g., anaturally-occurring sGC β1 protein). As discussed further herein, anH-NOX protein may optionally contain one or more mutations relative tothe corresponding naturally-occurring H-NOX protein. In someembodiments, the H-NOX protein includes one or more domains in additionto the H-NOX domain. In particular embodiments, the H-NOX proteinincludes one or more domains or the entire sequence from anotherprotein. For example, the H-NOX protein may be a fusion protein thatincludes an H-NOX domain and part or all of another protein, such asalbumin (e.g., human serum albumin). In some embodiments, only the H-NOXdomain is present.

A crystal structure of a prokaryotic O₂-binding H-NOX fromThermoanaerobacter tengcongensis (Nioche, P. et al. (Nov. 26, 2004).“Femtomolar Sensitivity of a NO Sensor From Clostridium Botulinum,”Science 306(5701):1550-1553; Pellicena, P. et al. (Aug. 31, 2004).“Crystal Structure of An Oxygen-Binding Heme Domain Related to SolubleGuanylate Cyclases,” Proc Natl. Acad Sci USA 101(35):12854-12859) showsthat a tyrosine side chain hydroxyl group makes a critical H-bond to theFe^(II)—O₂ moiety. This distal pocket hydrogen-bonding network,involving principally Y140, stabilizes an Fe^(II)—O₂ complex (FIG. 6B).This tyrosine is not present in H-NOX proteins that discriminate againstO₂ and only bind NO. For example, this hydrogen-bonding network ispredicted to be absent in the H-NOX proteins from sGCs and aerobicprokaryotes, suggesting this as a key molecular factor in the remarkableligand selectivity against O₂ displayed by these heme proteins. FIGS.7A-7G clearly demonstrate that the addition of a tyrosine in the distalpocket of a wild-type H-NOX protein that binds NO but not O₂ can enablethe mutant H-NOX protein to bind O₂. Thus, a tyrosine in the distal hemepocket of the H-NOX heme fold acts like a switch to turn on or off O₂binding.

As illustrated in FIGS. 6A and 6B, the structure of the porphyrin ishighly distorted. As illustrated in FIG. 6A, the conserved Y—S—R motifmakes hydrogen-bonding interactions with the propionic acid side chainsof the heme group. FIG. 6B, the conserved H102 is the proximal ligand tothe heme (FIG. 6B).

As used herein, a “protein” includes proteins and fragments of proteinswhether isolated from natural sources, produced by recombinanttechniques, or chemically synthesized. A protein may have one or moremodifications, such as a post-translational modification (e.g.,glycosylation, etc) or any other modification (e.g., PEGylation, etc).The protein may contain one or more non-naturally-occurring amino acids(e.g., such as an amino acid with a side chain modification). In variousembodiments, the H-NOX protein has at least about 50, 100, 150, 181,200, 250, 300, 350, 400, or more amino acids. In some embodiments, theH-NOX proteins may include from about 50 to about 600 amino acids, suchas about 100 to about 500 amino acids, about 150 to about 400 aminoacids, about 150 to about 300 amino acids, or about 175 to about 200amino acids.

Sources of H-NOX Proteins

H-NOX proteins from any genus or species can be used in thecompositions, kits, and methods described herein. In variousembodiments, the H-NOX protein is a protein from a mammal (e.g., aprimate (e.g., human, monkey, gorilla, ape, lemur, etc), a bovine, anequine, a porcine, a canine, or a feline), an insect, a yeast, or abacteria or is derived from such a protein. Exemplary mammalian H-NOXproteins include wild-type human and rat soluble guanylate cyclase (suchas the β1 subunit). Examples of H-NOX proteins include wild-typemammalian H-NOX proteins, e.g. H. sapiens, M musculus, C. familiaris, B.taurus and R. norvegicus; and wild-type non-mammalian vertebrate H-NOXproteins, e.g,. X laevis, O. latipes, O. curivatus, and F. rubripes.Examples of non-mammalian wild-type NO-binding H-NOX proteins includewild-type H-NOX proteins of D. melanogaster, A. gambiae, and M. sexta;examples of non-mammalian wild-type O₂-binding H-NOX proteins includewild-type H-NOX proteins of C. elegans gcy-31, gcy-32, gcy-33, gcy-34,gcy-35, gcy-36, and gcy-37; D. melanogaster CG14885, CG14886, andCG4154; and M. sexta beta-3; examples of prokaryotic wild-type H-NOXproteins include T. tengcongensis, V. cholera, V. fischerii, N.punctiforme, D. desulfuricans, L. pneumophila 1, L. pneumophila 2, andC. acetobutylicum.

NCBI Accession numbers for exemplary H-NOX proteins include thefollowing: Homo sapiens β1 [gi:2746083], Rattus norvegicus β1[gi:27127318], Drosophila melangaster β1 [gi:861203], Drosophilamelangaster CG14885-PA [gi:23171476], Caenorhabditis elegans GCY-35[gi:52782806], Nostoc punctiforme [gi:23129606], Caulobacter crescentus[gi:16127222], Shewanella oneidensis [gi:24373702], Legionellapneumophila (ORF 2) [CUCGC_(—)272624], Clostridium acetobutylicum[gi:15896488], and Thermoanaerobacter tengcongensis [gi:20807169].

Exemplary H-NOX protein also include the following H-NOX proteins thatare listed by their gene name, followed by their species abbreviationand Genbank Identifiers (such as the following protein sequencesavailable as of May 21, 2006; May 22, 2006; May 21, 2007; or May 22,2007, which are each hereby incorporated by reference in theirentireties): Npun5905_Npu_(—)23129606, alr2278_Ana_(—)17229770,SO2144_Sone_(—)24373702, Mdeg1343_Mde_(—)23027521,VCA0720_Vch_(—)15601476,CC2992_Ccr_(—)16127222,Rsph2043_Rhsp_(—)22958463 (gi:46192757), Mmc10739_Mcsp_(—)22999020,Tar4_Tte_(—)20807169,Ddes2822_Dde23475919,CAC3243_Cac_(—)15896488,gcy-31_Ce_(—)17568389,CG14885_Dm_(—)24647455,GUCY1B3_Hs_(—)4504215,HpGCS-beta1_Hpul_(—)14245738, Gycbeta100B_Dm_(—)24651577,CG4154_Dm_(—)24646993 (gi:NP_(—)650424.2, gi:62484298),gcy-32_Ce_(—)13539160,gcy-36_Ce_(—)17568391 (gi:32566352, gi:86564713),gcy-35_Ce-17507861 (gi:71990146), gcy-37_Ce_(—)17540904 (gi:71985505),GCY1a3_Hs_(—)20535603, GCY1a2-Hs_(—)899477, or GYCa-99B_Dm_(—)729270(gi:68067738) (Lakshminarayan et al. (2003). “Ancient conserved domainsshared by animal soluble guanylyl cyclases and bacterial signalingproteins,” BMG Genomics 4:5-13). The species abbreviations used in thesenames include Ana—Anabaena Sp; Ccr—Caulobacter crescentus;Cac—Clostridium acetobutylicum; Dde—Desulfovibrio desulfuricans;Mcsp—Magnetococcus sp.; Mde—Microbulbifer degradans; Npu—Nostocpunctiforme; Rhsp—Rhodobacter sphaeroides; Sone—Shewanella oneidensis;Tte—Thermoanaerobacter tengcongensis; Vch—Vibrio cholerae;Ce—Caenorhabditis elegans; Dm—Drosophila melanogaster;Hpul—Hemicentrotus pukherrimus; Hs—Homo sapiens.

Other exemplary H-NOX proteins include the following H-NOX proteins thatare listed by their organism name and Pfam database accession number(such as the following protein sequences available as of May 21, 2006;May 22, 2006; May 17, 2007; May 21, 2007; or May 22, 2007, which areeach hereby incorporated by reference in their entireties):Caenorhabditis briggsae Q622M5_CAEBR, Caenorhabditis briggsaeQ61P44_CAEBR, Caenorhabditis briggsae Q61R54_CAEBR, Caenorhabditisbriggsae Q61V90_CAEBR, Caenorhabditis briggsae Q61A94_CAEBR,Caenorhabditis briggsae Q60TP4_CAEBR, Caenorhabditis briggsaeQ60M10_CAEBR, Caenorhabditis elegans GCY37_CAEEL, Caenorhabditis elegansGCY31_CAEEL, Caenorhabditis elegans GCY36_CAEEL, Caenorhabditis elegansGCY32_CAEEL, Caenorhabditis elegans GCY35_CAEEL, Caenorhabditis elegansGCY34_CAEEL, Caenorhabditis elegans GCY33_CAEEL, Oryzias curvinotusQ7T040_ORYCU, Oryzias curvinotus Q75WFO_ORYCU, Oryzias latipesP79998_ORYLA, Oryzias latipes Q7ZSZ5_ORYLA, Tetraodon nigroviridisQ4SW38_TETNG, Tetraodon nigroviridis Q4RZ94_TETNG, Tetraodonnigroviridis Q4S6K5_TETNG, Fugu rubripes Q90VY5_FUGR Xenopus laevisQ6INK9_XENLA, Homo sapiens Q5T8J7_HUMAN, Homo sapiens GCYA2_HUMAN, Homosapiens GCYB2_HUMAN, Homo sapiens GCYB1_HUMAN, Gorilla gorillaQ9N193_(—)9PRIM, Pongo pygmaeus Q5RAN8_PONPY, Pan troglodytesQ9N192_PANTR, Macaca mulatta Q9N194_MACMU, Hylobates lar Q9N191_HYLLA,Mus musculus Q8BXH3 MOUSE, Mus musculus GCYB1_MOUSE, Mus musculusQ3UTI4_MOUSE, Mus musculus Q3UH83_MOUSE, Mus musculus Q6XE41_MOUSE, Musmusculus Q80YP4_MOUSE, Rattus norvegicus Q80WX7_RAT, Rattus norvegicusQ80WX8_RAT, Rattus norvegicus Q920Q1_RAT, Rattus norvegicus Q54A43_RAT,Rattus norvegicus Q80WY0_RAT, Rattus norvegicus Q80WY4_RAT, Rattusnorvegicus Q8CH85_RAT, Rattus norvegicus Q80WY5_RAT, Rattus norvegicusGCYB1_RAT, Rattus norvegicus Q8CH90_RAT, Rattus norvegicus Q91XJ7_RAT,Rattus norvegicus Q80WX9_RAT, Rattus norvegicus GCYB2_RAT, Rattusnorvegicus GCYA2_RAT, Canis familiaris Q4ZHR9_CANFA, Bos taurusGCYB1_BOVIN, Sus scrofa Q4ZHR7_PIG, Gryllus bimaculatus Q59HN5_GRYBI,Manduca sexta O77106_MANSE, Manduca sexta O76340_MANSE, Apis melliferaQ5UAF0_APIME, Apis mellifera Q5FAN0_APIME, Apis mellifera Q6L5L6_APIME,Anopheles gambiae str PEST Q7PYK9_ANOGA, Anopheles gambiae str PESTQ7Q9W6_ANOGA, Anopheles gambiae str PEST Q7QF31_ANOGA, Anopheles gambiaestr PEST Q7PS01_ANOGA, Anopheles gambiae str PEST Q7PFY2_ANOGA,Anopheles gambiae Q7KQ93_ANOGA, Drosophila melanogaster Q24086_DROME,Drosophila melanogaster GCYH_DROME, Drosophila melanogaster GCY8E DROME,Drosophila melanogaster GCYDA_DROME, Drosophila melanogasterGCYDB_DROME, Drosophila melanogaster Q9VA09_DROME, Drosophilapseudoobscura Q29CE1_DROPS, Drosophila pseudoobscura Q296C7_DROPS,Drosophila pseudoobscura Q296C8_DROPS, Drosophila pseudoobscuraQ29BU7_DROPS, Aplysia californica Q7YWK7_APLCA, Hemicentrotuspulcherrimus Q95NK5_HEMPU, Chlamydomonas reinhardtii, Q5YLC2_CHLRE,Anabaena sp Q8YUQ7_ANASP, Flavobacteria bacterium BBFL7 Q26GR8_(—)9BACT,Psychroflexus torquis ATCC 700755 Q1VQE5_(—)9FLAO, marine gammaproteobacterium HTCC2207 Q 1YPJ5_(—)9GAMM, marine gamma proteobacteriumHTCC2207 Q1YTK4_(—)9GAMM, Caulobacter crescentus Q9A451_CAUCR,Acidiphilium cryptum JF-5 Q2DG60ACICY, Rhodobacter sphaeroidesQ3J0U9_RHOS4, Silicibacter pomeroyi Q5LPV1_SILPO, Paracoccusdenitrificans PD1222, Q3PC67_PARDE, Silicibacter sp TM1040Q3QNY2_(—)9RHOB, Jannaschia sp Q28ML8_JANSC, Magnetococcus sp MC-1Q3XT27_(—)9PROT, Legionella pneumophila Q5WXP0_LEGPL, Legionellapneumophila Q5WTZ5_LEGPL, Legionella pneumophila Q5X268_LEGPA,Legionella pneumophila Q5X2R2_LEGPA, Legionella pneumophila subsppneumophila Q5ZWM9_LEGPH, Legionella pneumophila subsp pneumophilaQ5ZSQ8_LEGPH, Colwellia psychrelythraea Q47Y43_COLP3, Pseudoalteromonasatlantica T6c Q3CSZ5_ALTAT, Shewanella oneidensis Q8EF49_SHEON,Saccharophagus degradans Q21E20_SACD2, Saccharophagus degradansQ21ER7_SACD2, Vibrio angustum S14 Q1ZWE5_(—)9VIBR, Vibrio vulnificusQ8DAE2_VIBVU, Vibrio alginolyticus 12G01 Q1VCP6_VIBAL, Vibrio sp DAT722Q2FA22_(—)9VIBR, Vibrio parahaemolyticus Q87NJ1_VIBPA, Vibrio fischeriQ5E1F5_VIBF1, Vibrio vulnificus Q7MJS8_VIBVY, Photobacterium sp SKA34Q2C6Z5_(—)9GAMM, Hahella chejuensis Q2SFY7_HAHCH, Oceanospirillum spMED92 Q2BKV0_(—)9GAMM, Oceanobacter sp RED65 Q1NO35_(—)9GAMM,Desulfovibrio desulfuricans Q310U7_DESDG, Halothermothrix orenii H 168Q2AIW5_(—)9FIRM, Thermoanaerobacter tengcongensis Q8RBX6_THETN,Caldicellulosiruptor saccharolyticus DSM 8903 Q2ZH17_CALSA, Clostridiumacetobutylicum Q97E73_CLOAB, Alkaliphilus metalliredigenes QYMFQ3C763_(—)9CLOT, Clostridium tetani Q899J9_CLOTE, and Clostridiumbeijerincki NCIMB 8052 Q2WVN0_CLOBE. These sequences are predicted toencode H-NOX proteins based on the identification of these proteins asbelonging to the H-NOX protein family using the Pfam database asdescribed herein.

Additional 11-NOX proteins and nucleic acids, which may be suitable foruse in the pharmaceutical compositions and methods described herein, canbe identified using standard methods. For example, standard sequencealignment and/or structure prediction programs can be used to identifyadditional H-NOX proteins and nucleic acids based on the similarity oftheir primary and/or predicted protein secondary structure with that ofknown H-NOX proteins and nucleic acids. For example, the Pfam databaseuses defined alignment algorithms and Hidden Markov Models (such as Pfam21.0) to categorize proteins into families, such as the H-NOX proteinfamily (Pfam—A database of protein domain family alignments and HiddenMarkov Models, Copyright (C) 1996-2006 The Pfam Consortium; GNU LGPLFree Software Foundation, Inc., 59 Temple Place-Suite 330, Boston, Mass.02111-1307, USA). Standard databases such as the swissprot-trembldatabase (world-wide web at “expasy.org”, Swiss Institute ofBioinformatics Swiss-Prot group CMU-1 rue Michel Servet CH-1211 Geneva4, Switzerland) can also be used to identify members of the H-NOXprotein family. The secondary and/or tertiary structure of an H-NOXprotein can be predicted using the default settings of standardstructure prediction programs, such as PredictProtein (630 West, 168Street, BB217, New York, N.Y. 10032, USA). Alternatively, the actualsecondary and/or tertiary structure of an H-NOX protein can bedetermined using standard methods.

In some embodiments, the H-NOX protein has the same amino acid in thecorresponding position as any of following distal pocket residues in T.tengcongensis H-NOX: Thr4, Ile5, Thr8, Trp9, Trp67, Asn74, Ile75, Phe78,Phe82, Tyr140, Leu144, or any combination of two or more of theforegoing. In some embodiments, the H-NOX protein has a proline or anarginine in a position corresponding to that of Pro115 or Arg135 of T.tengcongensis H-NOX, respectively, based on sequence alignment of theiramino acid sequences. In some embodiments, the H-NOX protein has ahistidine that corresponds to His105 of R. norvegicus β1 H-NOX. In someembodiments, the H-NOX protein has or is predicted to have a secondarystructure that includes six alpha-helices, followed by two beta-strands,followed by one alpha-helix, followed by two beta-strands. Thissecondary structure has been reported for H-NOX proteins.

If desired, a newly identified H-NOX protein can be tested to determinewhether it binds heme using standard methods. The ability of an H-NOXprotein to function as an NO carrier can be tested by determiningwhether the H-NOX protein binds NO using standard methods, such as thosedescribed herein. If desired, one or more of the mutations describedherein can be introduced into the H-NOX protein to optimize itscharacteristics as an NO carrier. For example, one or more mutations canbe introduced to alter its NO dissociation constant, k_(off) for NO, k₁for NO, k₂ for NO, O₂ dissociation constant, NO stability, NOreactivity, rate of heme autoxidation, or any combination of two or moreof the foregoing. Standard techniques such as those described herein canbe used to measure these parameters.

As discussed herein, mutant H-NOX proteins (e.g., class I and class IImutants discussed below) may be derived by mutagenesis from these orother natural wild-type source sequences (e.g., the sequences listed inFIG. 2-4D or 8A-8DD or any other sequence described herein). As usedherein, “derived from” refers to the source of the protein into whichone or more mutations is introduced. For example, a protein that is“derived from a mammalian protein” refers to protein of interest thatresults from introducing one or more mutations into the sequence of awild-type (i.e., a sequence occurring in nature) mammalian protein.

Mutant H-NOX Proteins

As discussed further herein, an H-NOX protein may contain one or moremutations, such as a mutation that alters the NO dissociation constant,the k_(off) for NO, the O₂ dissociation constant, the k_(off) for O₂,the rate of heme autoxidation, the NO reactivity, the NO stability, orany combination of two or more of the foregoing compared to that of thecorresponding wild-type protein. Panels of engineered H-NOX proteins maybe generated by random mutagenesis followed by empirical screening forrequisite or desired dissociation constants, dissociation rates,NO-reactivity, stability, physio-compatibility, or any combination oftwo or more of the foregoing in view of the teaching provided hereinusing techniques as described herein and, additionally, as known by theskilled artisan. Alternatively, mutagenesis can be selectively targetedto particular regions or residues such as distal pocket residuesapparent from the experimentally determined or predictedthree-dimensional structure of an H-NOX protein (FIG. 1A herein; andsee, for example, Boon, E. M. et al. (2005). “Molecular Basis For NOSelectivity in Soluble Guanylate Cyclase,” Nature Chemical Biology1:53-59, which is hereby incorporated by reference in its entirety,particularly with respect to the sequences of wild-type and mutant H-NOXproteins) or evolutionarily conserved residues identified from sequencealignments (FIGS. 2-4D herein; and see, for example, Boon E. M. et al.(2005). “Molecular Basis For NO Selectivity in Soluble GuanylateCyclase,” Nature Chemical Biology 1:53-59, which is hereby incorporatedby reference in its entirety, particularly with respect to the sequencesof wild-type and mutant H-NOX proteins).

As used herein, a “mutant protein” means a protein with one or moremutations compared to a protein occurring in nature. In one embodiment,the mutant protein has a sequence that differs from that of all proteinsoccurring in nature. In various embodiments, the amino acid sequence ofthe mutant protein is at least about any of 10, 15, 20, 25, 30, 40, 50,60, 70, 80, 90, 95, 97, 98, 99, or 99.5% identical to that of thecorresponding region of a protein occurring in nature. In someembodiments, the mutant protein is a protein fragment that contains atleast about any of 25, 50, 75, 100, 150, 200, 300, or 400 contiguousamino acids from a full-length protein. Sequence identity can bemeasured, for example, using sequence analysis software with the defaultparameters specified therein (e.g., Sequence Analysis Software Packageof the Genetics Computer Group, University of Wisconsin BiotechnologyCenter, 1710 University Avenue, Madison, Wis. 53705). This softwareprogram matches similar sequences by assigning degrees of homology tovarious amino acids replacements, deletions, and other modifications.

As used herein, a “mutation” means an alteration in a reference nucleicacid or amino acid sequence occurring in nature. Exemplary nucleic acidmutations include an insertion, deletion, frameshift mutation, silentmutation, nonsense mutation, or missense mutation. In some embodiments,the nucleic acid mutation is not a silent mutation. Exemplary proteinmutations include the insertion of one or more amino acids (e.g., theinsertion of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acids), the deletion ofone or more amino acids (e.g., a deletion of N-terminal, C-terminal,and/or internal residues, such as the deletion of at least about any of5, 10, 15, 25, 50, 75, 100, 150, 200, 300, or more amino acids or adeletion of about any of 5, 10, 15, 25, 50, 75, 100, 150, 200, 300, or400 amino acids), the replacement of one or more amino acids (e.g., thereplacement of 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acids), orcombinations of two or more of the foregoing. An exemplary functionaltruncation of an H-NOX protein includes residues 1-385 of the β1sequence. In some embodiments, a mutant protein has at least one aminoacid alteration compared to a protein occurring in nature. In someembodiments, a mutant nucleic acid sequence encodes a protein that hasat least one amino acid alteration compared to a protein occurring innature. In some embodiments, the nucleic acid is not a degenerateversion of a nucleic acid occurring in nature that encodes a proteinwith an amino acid sequence identical to a protein occurring in nature.The nomenclature used in referring to a particular amino acid mutationfirst identifies the wild-type amino acid, followed by the residuenumber and finally the substitute amino acid. For example, Y140L meansthat tyrosine has been replaced by a leucine at residue number 140.

An “evolutionary conserved mutation” is the replacement of an amino acidin one protein by an amino acid in the corresponding position of anotherprotein in the same protein family. Exemplary evolutionary conservedmutations (also denoted class I mutations) are listed in Table 1A. InTable 1 A, mutations are numbered/annotated according to the sequence ofhuman β1 H-NOX, but are analogous for all H-NOX sequences. Thus, thecorresponding position in any other H-NOX protein can be mutated to theindicated residue. For example, Phe4 of human β1 H-NOX can be mutated toa tyrosine since other H-NOX proteins have a tyrosine in this position.The corresponding phenylalanine residue can be mutated to a tyrosine inany other H-NOX protein. In particular embodiments, the one or moremutations are confined to evolutionarily conserved residues. In someembodiments, the one or more mutations may include at least oneevolutionarily conserved mutation and at least one non-evolutionarilyconserved mutation. If desired, these mutant H-NOX proteins aresubjected to empirical screening for NO/O₂ dissociation constants,NO-reactivity, stability, and physio-compatibility in view of theteaching provided herein.

TABLE 1A Exemplary Class I H—NOX mutations targeting evolutionaryconserved residues F4Y Q30G I145Y F4L E33P I145H H7G N61G K151E A8E C78HI157F L9W A109F E183F

In some embodiments, the mutation is a distal pocket mutation, such asmutation of a residue in alpha-helix A, D, E, or G (Pellicena, P. et al.(Aug. 31, 2004). “Crystal Structure of An Oxygen-Binding Heme DomainRelated to Soluble Guanylate Cyclases,” Proc Natl. Acad Sci USA101(35):12854-12859). Exemplary distal pocket mutations (also denotedclass II mutations) are listed in Table 1B. In Table 1B, mutations arenumbered/annotated according to the sequence of human β1 H-NOX, but areanalogous for all H-NOX sequences. Because several substitutions provideviable mutations at each recited residue, the residue at each indicatedposition can be changed to any other naturally ornon-naturally-occurring amino acid (denoted “X”). Such mutations canproduce H-NOX proteins with a variety of desired affinity, stability,and reactivity characteristics.

TABLE 1B Exemplary Class II H—NOX mutations targeting distal pocketresidues V8X M73X I145X L9X F77X I149X F70X C78X

In particular embodiments, the mutation is a heme distal pocketmutation. As described herein, a crucial molecular determinant thatprevents O₂ binding in NO-binding members of the H-NOX family is thelack of a H-bond donor in the distal pocket of the heme. Accordingly, insome embodiments, the mutation alters H-bonding between the H-NOX domainand the ligand within the distal pocket. In some embodiments, themutation disrupts an H-bond donor of the distal pocket and/or impartsreduced O₂ ligand-binding relative to the corresponding wild-type H-NOXdomain. Exemplary distal pocket residues include Thr4, Ile5, Thr8, Trp9,Trp67, Asn74, Ile75, Phe78, Phe82, Tyr140, and Leu144 of T.tengcongensis H-NOX and the corresponding residues in any other H-NOXprotein.

Residues that are not in the distal pocket can also affect thethree-dimensional structure of the heme group; this structure in turnaffects the binding of O₂ and NO to iron in the heme group. Accordingly,in some embodiments, the H-NOX protein has one or more mutations outsideof the distal pocket. Examples of residues that can be mutated but arenot in the distal pocket include Pro115 and Arg135 of T. tengcongensisH-NOX. In some embodiments, the mutation is in the proximal pocket whichincludes His 105 as a residue that ligates to the heme iron.

In some embodiments when two or more mutations are present; at least onemutation is in the distal pocket, and at least one mutation is outsideof the distal pocket (e.g., a mutation in the proximal pocket). In someembodiments, all the mutations are in the distal pocket.

In some embodiments, the amino acid sequence of the H-NOX protein is notidentical to the sequence of a protein that is produced by an organismin nature. In some embodiments, the amino acid sequence of the H-NOXprotein is not identical to a sequence found in any database on May 21,2006 or May 22, 2006 (such as all known sequences predicted or known tobe an H-NOX nucleic acid or amino acid sequence). In some embodiments,the amino acid sequence of the H-NOX protein is not identical to asequence found in any database on May 21, 2007 or May 22, 2007 (such asall known sequences predicted or known to be an H-NOX nucleic acid oramino acid sequence).

To reduce the immunogenicity of H-NOX proteins derived from sourcesother than humans, amino acids in an H-NOX protein can be mutated to thecorresponding amino acids in a human H-NOX. For example, one or moreamino acids on the surface of the tertiary structure of a non-humanH-NOX protein can be mutated to the corresponding amino acid in a humanH-NOX proteins. In some variations, mutation of one or more surfaceamino acids may be combined with mutation of two or more distal pocketresidues, mutation of one or more residues outside of the distal pocket(e.g., a mutation in the proximal pocket), or combinations of two ormore of the foregoing.

Exemplary mutations are shown in Table 2. In addition, any of theresidues listed in Table 2 can be mutated to any other amino acid. Theinvention also relates to any combination of mutation described herein,such as double, triple, or higher multiple mutations. For example,combinations of any of the mutations described herein can be made in thesame H-NOX protein. Note that mutations in equivalent positions in othermammalian or non-mammalian H-NOX proteins are also encompassed by thisinvention. If desired, residues other than the ones mentioned in Table 2can also be mutated. Exemplary mutant H-NOX proteins comprise one ormore mutations that impart altered NO or O₂ ligand-binding relative tothe corresponding wild-type H-NOX domain and are operative as aphysiologically compatible mammalian NO blood gas carrier.

In Table 2 and all subsequent tables, the residue number for a mutationindicates the position in the sequence of the particular H-NOX proteinbeing described. For example, T. tengcongensis 15A refers to thereplacement of isoleucine by alanine at the fifth position in T.tengcongensis H-NOX. The same isoleucine to alanine mutation can be madein the corresponding residue in any other H-NOX protein (this residuemay or may not be the fifth residue in the sequence of other H-NOXproteins). Since the amino acid sequences of mammalian β1 H-NOX domainsdiffer by at most two amino acids, mutations that produce desirablemutant H-NOX proteins when introduced into wild-type rat β1 H-NOXproteins are also expected to produce desirable mutant H-NOX proteinswhen introduced into wild-type β1 H-NOX proteins from other mammals,such as humans.

In some embodiments, the H-NOX protein has at least one mutation inwhich a residue that corresponds to Ile5, Trp9, Asn74, Pro115, Arg135,or Tyr140 of T. tengcongensis H-NOX, I145 of β1(1-385), or Phe142 of L.pneumophila 2 is replaced by any other amino acid. In some embodiments,the H-NOX protein has at least two mutations, wherein at least onemutation is the replacement of a residue that corresponds to Ile5, Trp9,Asn74, Pro115, Arg135, or Tyr140 of T. tengcongensis H-NOX, I145 ofβ1(1-385), or Phe142 of L. pneumophila 2 by any other amino acid. Insome embodiments, the mutation in the H-NOX protein corresponds to a I5Amutation, a 15L mutation, a W9F mutation, a Y140F mutation, a Y140Lmutation, a Y140H mutation, a W9F Y140H double mutation, or a F78Y Y140Fdouble mutation of T. tengcongensis or a I145Y mutation of β1. In someembodiments, the mutation in the H-NOX protein corresponds to a W9Ymutation, a W9H mutation, a W9N mutation, a N74H mutation, a N74Emutation, a N74A mutation, a P115A mutation, a R135Q mutation, a 15LP115A double mutant, a N74A Y140H double mutant, or a W9F N74A doublemutant of T. tengcongensis. In some embodiments, at least one C-terminalamino acid (such as at least about 50 contiguous C-terminal amino acidsor between about 25 to about 200 contiguous C-terminal amino acids) inthe H-NOX protein has been removed compared to the correspondingwild-type protein (such as R. norvegicus or H. sapiens β1).

TABLE 2 Exemplary H—NOX mutants from T. tengcongensis (Tt), L.pneumophila (Lp), D. desulfuricans (Dd), V. cholera (Vc), N. punctiforme(Np), C. botulinium (Cb), C. acetobutylicum, (Ca), rat, human, C.elegans (Ce). Other Tt Lp Dd Bacteria Rat Human Worm Tt H—NOX L2 H—NOXDd H—NOX Vc H—NOX β1(1-385) β1(1-385) Ce GCY- (728- 35(1-252) 899) TtH—NOX L2 F142Y Dd Y139L Np H—NOX β1(1-385) β1(1-385) His6 I145Y I145Y TtI5A L2 F9W- Cb H—NOX β1(1-385) β1(1-385) F142Y (1- I145H I145H 175) TtI5L L1 H—NOX Cb H—NOX β1(1-385) β1(1-385) (1- C78Y C78Y 186) Tt I5L- L1F142Y Ca H—NOX β1(1-194) β1(1-194) P115A (1- 197) Tt W9F Ca H—NOX β1H105F β1 H105F (1- 183) Tt W9F- β1 H105G β1 H105G Y140L Tt W9F-β1(1-194) β1(1-194) Y140H I145Y I145Y Tt W9F- β1(1-194) β1(1-194) N74AL9W-I145Y L9W- I145Y Tt W9Y β2(1-217) β2(1-217) Tt W9N β2(1-217)β2(1-217) Tt W9H I142Y I142Y Tt N74E Tt N74A Tt N74H Tt N74A- Y140H TtI75F His6 Tt F78Y- Y140L Tt F78Y- Y140F Tt P115A Tt R135Q His6 Tt Y140FTt Y140L Tt Y140H Tt Y140A Tt L144F His6Modifications to H-NOX Proteins

Any of the wild-type or mutant H-NOX proteins can be modified and/orformulated using standard methods to enhance therapeutic or industrialapplications. For example, and particularly as applied to heterologousengineered H-NOX proteins, a variety of methods are known in the art forinsulating such agents from immune surveillance, including crosslinking,PEGylation, carbohydrate decoration, etc. (e.g., Rohlfs, R. J. et al.(May 15, 1998). “Arterial Blood Pressure Responses to Cell-FreeHemoglobin Solutions And The Reaction With Nitric Oxide,” J. Biol. Chem.273(20):12128-12134; Migita, R. et al. (June 1997). “Blood Volume AndCardiac Index in Rats After Exchange Transfusion With Hemoglobin-BasedOxygen Carriers,” J. Appl. Physiol. 82(6):1995-2002; Vandegriff, K. D.et al. (Aug. 15, 2004). “Kinetics of NO and O₂ Binding to a MaleimidePoly(ethylene glycol)-Conjugated Human Haemoglobin,” Biochem J. 382(Pt1):183-189, which are each hereby incorporated by reference in theirentireties, particularly with respect to the modification of proteins)as well as other techniques known to the skilled artisan. Fusing anH-NOX protein with a human protein such as human serum albumin canincrease the serum half-life, viscosity, and colloidal oncotic pressure.In some embodiments, an H-NOX protein is modified during or after itssynthesis to decrease its immunogenicity and/or to increase its plasmaretention time. H-NOX proteins can also be encapsulated (such asencapsulation within liposomes or nanoparticles).

Characteristics of Wild-type and Mutant H-NOX Proteins

As described herein, a large number of diverse H-NOX mutant proteinsproviding ranges of NO dissociation constants, O₂ dissociationconstants, NO k_(off), O₂ k_(off), NO reactivity, and stability havebeen generated. In some embodiments, an H-NOX protein has a similar orimproved NO dissociation constant, O₂ dissociation constant, NO k_(off),O₂ k_(off), NO reactivity, autoxidation rate, plasma retention time, orany combination of two or more of the foregoing compared to anycurrently used compound for delivering NO, such as any organic nitratefor bioconversion into NO.

As discussed above, the intrinsic low NO reactivity (and high NOstability) makes wild-type and mutant H-NOX proteins desirable NOcarriers because of the lower probability of inactivation of H-NOXproteins by NO in the presence of O₂. In some embodiments, an H-NOXprotein has a low affinity for O₂ (such as an O₂ dissociation constantof at least about 1 μM at 37° C.) or no detectable affinity for O₂.Since little, if any, O₂ is bound to the H-NOX protein, there is minimaloxidation by NO of O₂ bound to the heme of the H-NOX protein. Thus,minimal NO, O₂, and H-NOX protein is inactivated by this NO oxidation.Thus, more NO can be delivered to desired sites in an individual andless O₂ that could be used by the tissues in the individual isdestroyed.

As used herein, “hemoglobin” means a protein or a mutant thereof fromthe well-characterized family of hemoglobins, which are iron-containingO₂-transport metalloproteins in red blood cells. Purified, stroma-free,human hemoglobin has a kinetic K_(D) for O₂ of about 200-500 nM. Thisvalue is subunit dependent.

By “a 6-coordinate Fe^(II)—NO complex” is meant a 6-coordinateferrous-nitrosyl that produces a UV-Vis Soret peak at approximately416-422 nm, as described, e.g., by Boon, E. M. et al., (August 2006),“Nitric Oxide Binding to Prokaryotic Homologs of the Solube GuanylateCyclase β1 H0NOX Domain,” J. Biol. Chem. 281(31): 21892-21902, which ishereby incorporated by reference in its entirety, particularly withrespect to the determination of the percentage of a H-NOX protein samplethat contains a 6-coordinate Fe^(II)—NO complex and the percentage of aH-NOX protein sample that contains a 5-coordinate Fe^(II)—NO complex.

By “a 5-coordinate Fe^(II)—NO complex” is meant a 5-coordinateferrous-nitrosyl that produces a UV-Vis Soret peak at approximately397-400 nm, as described, e.g., by Boon, E. M. et al., (August 2006),“Nitric Oxide Binding to Prokaryotic Homologs of the Solube GuanylateCyclase β1 HONOX Domain,” J. Biol. Chem. 281(31): 21892-21902, which ishereby incorporated by reference in its entirety, particularly withrespect to the determination of the percentage of a H-NOX protein samplethat contains a 6-coordinate Fe^(II)—NO complex and the percentage of aH-NOX protein sample that contains a 5-coordinate Fe^(II)—NO complex.

As used herein, a “K_(off)” means a dissociation rate, such as the rateof release of NO or O₂ from a protein. A lower numerical lower k_(off)indicates a slower rate of dissociation. For an H-NOX protein with a6-coordinate Fe^(II)—NO complex, the k_(off) for NO is calculated asdescribed by Boon, E. M. et al., (August 2006), “Nitric Oxide Binding toProkaryotic Homologs of the Solube Guanylate Cyclase β1 H0NOX Domain,”J. Biol. Chem. 281(31): 21892-21902 and Boon, E. M. et al. (2005).“Molecular Basis For NO Selectivity in Soluble Guanylate Cyclase,”Nature Chemical Biology 1:53-59, which are each hereby incorporated byreference in their entireties, particularly with respect to thecalculation of NO k_(off) for H-NOX proteins. For an H-NOX protein witha 5-coordinate Fe^(II)—NO complex, the k_(off) for NO is described bythe k₁ for NO and the k₂ for NO, as described by Winger, J. A. et al.,(January 2007) “Dissociation of Nitric Oxide from Soluble GuanylateCyclase and Heme-Nitric Oxide/Oxygen Binding Domain Constructs” J. Biol.Chem. 282(2): 897-907, which is hereby incorporated by reference in itsentirety, particularly with respect to the calculation of NO k_(off), NOk₁, and NO k₂ for H-NOX proteins. For an H-NOX protein that contains amixture of 5-coordinate and 6-coordinate F^(II)—NO complexes, thek_(off) for NO is described by the k₁ for NO and the k₂ for NO, asdescribed by Winger, J. A. et al., (January 2007) “Dissociation ofNitric Oxide from Soluble Guanylate Cyclase and Heme-Nitric Oxide/OxygenBinding Domain Constructs” J. Biol. Chem. 282(2): 897-907, which ishereby incorporated by reference in its entirety, particularly withrespect to the calculation of NO k_(off), NO k₁, and NO k₂ for H-NOXproteins.

In some embodiments, the k_(off), k₁, or k₂ for NO for the H-NOX proteinis between about 1×10⁻⁴ s⁻¹ to about 10 s⁻¹ at 37° C., such as betweenabout 1×10⁻⁴ s⁻¹, about 1×10⁻⁴ s⁻¹ to about 0.007 s⁻¹, about 0.005 s⁻¹to about 0.011 s⁻¹, or about 1×10⁻³ s⁻¹ at 37° C. In variousembodiments, the k_(off) for O₂ for an H-NOX protein is between about 1to about 1,000 s⁻¹ at 37° C., such as about 1 to about 50 s⁻¹, about 50to about 100 s⁻¹, about 100 to about 250 s⁻¹, about 250 to about 500s⁻¹, about 500 to about 750 s⁻¹, or about 750 to about 1,000 s⁻¹ at 37°C.

By a “k_(on)” is meant an association rate, such as the rate of bindingof NO or O₂ to a protein. A lower numerical lower K_(off) indicates aslower rate of association. In various embodiments, the k_(on) for O₂for an H-NOX protein is between about 0.14 to about 60 μM⁻¹ s⁻¹ at 20°C., such as about 6 to about 60 μM⁻¹ s⁻¹, about 6 to 12 μM⁻¹ s⁻¹, about15 to about 60 μM⁻¹ s⁻¹, about 5 to about 18 μM⁻s⁻¹, or about 6 to about15 μM⁻¹ s⁻¹.

By “dissociation constant” is meant a “kinetic dissociation constant” ora “calculated dissociation constant.” A “kinetic dissociation constant”or “K_(D)” means a ratio of kinetic off-rate (k_(off)) to kineticon-rate (k_(on)), such as a K_(D) value determined as an absolute valueusing standard methods (e.g., standard spectroscopic, stopped-flow, orflash-photolysis methods) including methods known to the skilled artisanand/or described herein. “Calculated dissociation constant” or“calculated K_(D)” refers to an approximation of the kineticdissociation constant based on a measured k_(off). For the calculatedK_(D) for NO, the value for the k_(on) for NO for an H-NOX protein isassumed to be 710 μM⁻¹ s⁻¹, which is a reported k_(on) for β1(1-385)that was measured at 4° C. and does not increase significantly at 37° C.(Zhao, et. al., (1999). “A Molecular Basis for Nitric Oxide Sensing bySoluble Guanylate Cyclase,” PNAS. 96:14753-14758, which is herebyincorporated by reference in its entirety, particularly with respect tothe calculation of NO k_(on) for H-NOX proteins). For the calculatedK_(D) for O₂, a value for the k_(on) is derived via the correlationbetween kinetic K_(D) and k_(off) as described herein.

In various embodiments, the kinetic or calculated K_(D) for NO bindingby an H-NOX protein is within about 0.01 to about 100-fold of that ofhemoglobin under the same conditions (such as at 20° C.), such asbetween about 0.1 to about 10-fold or between about 0.5 to about 2-foldof that of hemoglobin under the same conditions (such as at 20° C.). Insome embodiments, the NO dissociation constant of the H-NOX protein isbetween about 0.1 to about 20 pM at 37° C., such as about 0.5 to about15, about 0.5 to about 12, about 0.7 to about 4, or about 0.7 to about 3at 37° C., In some embodiments, the NO dissociation constant of theH-NOX protein is at least about 0.1 pM at 37° C., such as at least aboutany of 0.5, 1, 3, 5, 10, 12, 50, 100, 400, 500, 1000, 2000, 3000, or4000 pM at 37° C. In some embodiments, the NO dissociation constant ofthe H-NOX protein is less than about 5000 pM at 37° C., such as lessthan about any of 4000 pM, 3000 pM, 2000 pM, 1000 pM, 500 pM, 400 pM,100 pM, 50 pM, 12 pM, 10 pM, 5 pM, 3 pM, or 1 pM at 37° C.

In various embodiments, the kinetic or calculated K_(D) for O₂ bindingby an H-NOX protein is within about 0.01 to about 100-fold of that ofhemoglobin under the same conditions (such as at 20° C.), such asbetween about 0.1 to about 10-fold or between about 0.5 to about 2-foldof that of hemoglobin under the same conditions (such as at 20° C.). Insome embodiments, the O₂ dissociation constant of the H-NOX protein itat least about 1 μM at 37° C., such as at least about any of 5 μM, 10μM, 20 μM, 30 μM, 40 μM, 50 μM, 60 μM, 70 μM, 80 μM, 90 μM, or 100 μM at37° C. In some embodiments, there is no detectable binding to O₂ at 37°C., such as the lack of detectable O₂ binding using UV-visiblespectroscopy as described herein (e.g., a lack of an observable peak at˜418 nm in the presence of O₂, such as when the Soret peak remains at˜431 nm as seen in the absence of O₂ or when the Soret peak shifts to˜410 nm due to oxidized protein).

As used herein, “NO affinity” is a qualitative term that refers to thestrength of NO binding to a protein (such as binding to a heme group orto an oxygen bound to a heme group associated with a protein). Thisaffinity is affected by both the k_(off) and k_(on) for NO. Anumerically lower NO K_(D) value means a higher affinity. “Oxygenaffinity” is a qualitative term that refers to the strength of oxygenbinding to the heme moiety of a protein. This affinity is affected byboth the k_(off) and k_(on) for oxygen. A numerically lower oxygen K_(D)value means a higher affinity.

As used herein, “NO stability” refers to the stability or resistance ofa protein to oxidation by NO in the presence of oxygen. For example, theability of the protein to not be oxidized when bound to NO in thepresence of oxygen is indicative of the protein's NO stability. In someembodiments, less than about any of 50, 40, 30, 10, or 5% of an H-NOXprotein is oxidized after incubation for about any of 1, 2, 4, 6, 8, 10,15, or 20 hours at 20° C.

As used herein, “NO reactivity” refers to the rate at which iron in theheme of a heme-binding protein is oxidized by NO in the presence ofoxygen at a concentration of 2 μM protein. A lower numerical value forNO reactivity in units of s⁻¹ indicates a lower NO reactivity. Invarious embodiments, the NO reactivity of an H-NOX protein is less thanabout 700 s⁻¹ at 20° C., such as less than about 600 s⁻¹, 500 s⁻¹, 400s⁻¹, 300 s⁻¹, 200 s⁻¹, 100 s⁻¹, 75 s⁻¹, 25 s⁻¹, 20 s⁻¹, 10 s⁻¹, 50 s⁻¹,3 s⁻¹, 2 s⁻¹, 1.8 s⁻¹, 1.5 s⁻¹, 1.2 s⁻¹, 1.0 s⁻¹, 0.8 s⁻¹, 0.7 s⁻¹, or0.6 s⁻¹ at 20° C. In various embodiments, the NO reactivity of an H-NOXprotein is between about 0.1 to about 600 s⁻¹ at 20° C., such as betweenabout 0.5 to about 400 s⁻¹, about 0.5 to about 100 s⁻¹, about 0.5 toabout 50 s⁻¹, about 0.5 to about 10 s⁻¹, about 1 to about 5 s⁻¹, orabout 0.5 to about 2.1 s⁻¹ at 20° C. In various embodiments, thereactivity of an H-NOX protein is at least about 10, 100, 1,000, or10,000 fold lower than that of hemoglobin under the same conditions,such as at 20° C.

As used herein, an “autoxidation rate” refers to the rate at which ironin the heme of a heme-binding protein is autoxidized. A lower numericalautoxidation rate in units of s⁻¹ indicates a lower autoxidation rate.In various embodiments, the rate of heme autoxidation of an H-NOXprotein is less than about 1.0 h⁻¹ at 37° C., such as less than aboutany of 0.9 h⁻¹, 0.8 h⁻¹, 0.7 h⁻¹, 0.6 h⁻¹, 0.5 h⁻¹, 0.4 h⁻¹, 0.3 h⁻¹,0.2 h⁻¹, 0.1 h⁻¹, or 0.05 h⁻¹ at 37° C. In various embodiments, the rateof heme autoxidation of an H-NOX protein is between about 0.006 to about5.0 at 37° C., such as about 0.006 to about 1.0 h⁻¹, 0.006 to about 0.9h⁻¹, or about 0.06 to about 0.5 h⁻¹ at 37° C.

In various embodiments, a mutant H-NOX protein has (a) an NO or O₂dissociation constant, association rate (k_(on) for NO or O₂), ordissociation rate (k_(off) for NO or O₂) within 2 orders of magnitude ofthat of hemoglobin, (b) has an NO affinity weaker (e.g., at least about10-fold, 100-fold, or 1000-fold weaker) than that of sGC β1 (c) an NOreactivity with bound O₂ at least 1000-fold less than hemoglobin, (d) anin vivo plasma retention time at least 2, 10, 100, or 1000-fold higherthan that of hemoglobin, or (e) any combination of two or more of theforegoing.

Exemplary suitable NO carriers provide dissociation constants within twoorders of magnitude of that of hemoglobin, i.e. between about 0.01 and100-fold, such as between about 0.1 and 10-fold, or between about 0.5and 2-fold of that of hemoglobin. A variety of established techniquesmay be used to quantify dissociation constants, such as the techniquesdescribed herein (Boon, E. M. et al. (2005). “Molecular Basis For NOSelectivity in Soluble Guanylate Cyclase,” Nature Chem. Biol. 1:53-59;Boon, E. M. et al. (October 2005). “Ligand Discrimination in SolubleGuanylate Cyclase and the H-NOX Family of Heme Sensor Proteins,” Curr.Opin. Chem. Biol. 9(5):441-446; Boon, E. M. et al. (2005). “LigandSpecificity of H-NOX Domains: From sGC to Bacterial NO Sensors,” J.Inorg. Biochem. 99(4):892-902), Vandegriff, K. D. et al. (Aug. 15,2004). “Kinetics of NO and O₂ Binding to a Maleimide Poly(ethyleneglycol)-Conjugated Human Haemoglobin,” Biochem J. 382(Pt 1):183-189,which are each hereby incorporated by reference in their entireties,particularly with respect to the measurement of dissociation constants),as well as those known to the skilled artisan. Exemplary NO carriersprovide low or minimized NO reactivity of the H-NOX protein with boundO₂, such as an NO reactivity lower than that of hemoglobin. In someembodiments, the NO reactivity is much lower, such as at least about 10,100, 1,000, or 10,000-fold lower than that of hemoglobin. A variety ofestablished techniques may be used to quantify NO reactivity (Boon, E.M. et al. (2005). “Molecular Basis For NO Selectivity in SolubleGuanylate Cyclase,” Nature Chem. Biol. 1:53-59; Boon, E. M. et al.(October 2005). “Ligand Discrimination in Soluble Guanylate Cyclase andthe H-NOX Family of Heme Sensor Proteins,” Curr. Opin. Chem. Biol.9(5):441-446; Boon, E. M. et al. (2005). “Ligand Specificity of H-NOXDomains: From sGC to Bacterial NO Sensors,” J. Inorg. Biochem.99(4):892-902), Vandegriff, K. D. et al. (Aug. 15, 2004). “Kinetics ofNO and O₂ Binding to a Maleimide Poly(ethylene glycol)-Conjugated HumanHaemoglobin,” Biochem J. 382(Pt 1):183-189, which are each herebyincorporated by reference in their entireties, particularly with respectto the measurement of NO reactivity) as well as those known to theskilled artisan. Because wild-type T. tengcongensis H-NOX has such a lowNO reactivity, other wild-type H-NOX proteins and mutant H-NOX proteinsmay have a similar low NO reactivity. For example, T. tengcongensisH-NOX Y140H has an NO reactivity similar to that of wild-type T.tengcongensis H-NOX.

Exemplary mutants for NO delivery have an NO affinity weaker, preferablyat least 10-fold, 100-fold, or 1000-fold weaker than that of sGC β1. Fortherapeutic NO delivery (e.g., during/following a heart attack, openheart surgery, or stroke) a range of engineered H-NOX proteins withvarying affinities are empirically tested for efficacy in particulardisease states, with a range in some embodiments of NO affinities of 0.1to 1000 nM.

In addition, suitable NO carriers provide high or maximized stability,particularly in vivo stability. A variety of stability metrics may beused, such as oxidative stability (e.g., stability to autoxidation oroxidation by NO), temperature stability, and in vivo stability. Avariety of established techniques may be used to quantify stability,such as the techniques described herein (Boon, E. M. et al. (2005).“Molecular Basis For NO Selectivity in Soluble Guanylate Cyclase,”Nature Chem. Biol. 1:53-59; Boon, E. M. et al. (October 2005). “LigandDiscrimination in Soluble Guanylate Cyclase and the H-NOX Family of HemeSensor Proteins,” Curr. Opin. Chem. Biol. 9(5):441-446; Boon, E. M. etal. (2005). “Ligand Specificity of H-NOX Domains: From sGC to BacterialNO Sensors,” J. Inorg. Biochem. 99(4):892-902), as well as those knownto the skilled artisan. For in vivo stability in plasma, blood, ortissue, exemplary metrics of stability include retention time, rate ofclearance, and half-life. H-NOX proteins from thermophilic organisms areexpected to be stable at high temperatures. In various embodiments, theplasma retention times are at least about 2-, 10-, 100-, or 1000-foldgreater than that of hemoglobin (e.g. Bobofchak, K. M. et al. (August2003). “A Recombinant Polymeric Hemoglobin With Conformational,Functional, And Physiological characteristics of an in vivo 02transporter,” Am. J. Physiol. Heart Circ. Physiol. 285(2):H549-H561). Aswill be appreciated by the skilled artisan, hemoglobin-based carriersare limited by the rapid clearance of cell-free hemoglobin from plasmadue the presence of receptors for hemoglobin that remove cell-freehemoglobin from plasma. Since there are no receptors for H-NOX proteinsin plasma, wild-type and mutant H-NOX proteins are expected to have alonger plasma retention time than that of hemoglobin. If desired, theplasma retention time can be increased by PEGylating or crosslinking anH-NOX protein or fusing an H-NOX protein with another protein usingstandard methods (such as those described herein and those known to theskilled artisan).

In various embodiments, the NO dissociation constant of the H-NOXprotein is within 2 orders of magnitude of that of hemoglobin, and theNO reactivity of the H-NOX protein is at least 10-fold lower than thatof hemoglobin. In some embodiments, the k_(off), k₁ or k₂ for NO of theH-NOX protein is between about 1×10⁴ s⁻¹ to about 10 s⁻¹ at 37° C., andthe O₂ dissociation constant of the H-NOX protein is at least about 1 μMat 37° C. In some embodiments, the k_(off), k₁, or k₂ for NO of theH-NOX protein is between about 1×10⁻⁴ s⁻¹ to about 10 s⁻¹ at 37° C., andthe O₂ dissociation constant of the H-NOX protein is at least about 1 μMat 37° C. In some embodiments, the k_(off), k₁, or k₂ for NO of theH-NOX protein is between about 1×10⁻⁴ s⁻¹ to about 10 s⁻¹ at 37° C., andthe NO reactivity of the H-NOX protein is less than about 700 s⁻¹ at 20°C. (e.g., less than about 600 s⁻¹, 500 s⁻¹, 100 s⁻¹, 20 s⁻¹, or 1.8 s⁻¹at 20° C.). In some embodiments, the O₂ dissociation constant of theH-NOX protein is at least about 1 μM at 37° C., and the NO reactivity ofthe H-NOX protein is less than about 700 s⁻¹ at 20° C. (e.g., less thanabout 600 s⁻¹, 500 s⁻¹, 100 s⁻¹, 20 s⁻¹, or 1.8 s⁻¹ at 20° C.). In someembodiments, the k_(off), k₁, or k₂ for NO of the H-NOX protein isbetween about 1×10⁻⁴ s⁻¹ to about 10 s⁻¹ at 37° C., and the rate of hemeautoxidation of the H-NOX protein is less than about 1 h⁻¹ at 37° C. Insome embodiments, the O₂ dissociation constant of the H-NOX protein isat least about 1 μM at 37° C., and the rate of heme autoxidation of theH-NOX protein is less than about 1 h⁻¹ at 37° C. In some embodiments,the rate of heme autoxidation of the H-NOX protein is less than about 1h⁻¹ at 37° C., and the NO reactivity of the H-NOX protein is less thanabout 700 s⁻¹ at 20° C. (e.g., less than about 600 s⁻¹, 500 s⁻, 100 s⁻¹,20 s⁻¹, or 1.8 s⁻¹ at 20° C.). In some embodiments, the viscosity of theH-NOX protein solution is between 1 and 4 centipoise (cP). In someembodiments, the colloid oncotic pressure of the H-NOX protein solutionis between 20 and 50 mm Hg.

Table 3 lists exemplary sizes, oxygen affinities, autoxidationstabilities, NO reactivity rates, and modifications for wild-type andmutant H-NOX proteins. In Table 3, the vehicle size refers to themolecular weight of a modified (e.g., PEGylated) or unmodified H-NOXprotein.

TABLE 3 Exemplary Embodiments for H—NOX proteins Oxygen Stability NOreactivity Particle Vehicle size Affinity (autoxidation) NO affinity(s⁻¹) decoration   >1 MD at least 1 μM  1 hour  1 pM 0.01 to 0.1Cross-liking  0.5 kD to 1 MD at least 10 μM  1 h to 12 h 500 pM 0.1 to1  PEGylation  0.1 kD to 0.5 kD at least 50 μM 12 h to 48 h  1 nM  1 to10 Encapsulation 0.01 kD to 0.1 kD at least 75 μM 48 h to 2 weeks  1 μM 10 to 100

Exemplary data for particular mutants are reported in Tables 4-14. InTables 4-14, β1 and B2 refer to proteins derived from rat H-NOXproteins. Since the amino acid sequences of mammalian β1 H-NOX domainsdiffer by at most two amino acids, similar results are expected for thecorresponding mutations in other mammalian β1 H-NOX proteins, such ashuman β1.

Table 4 demonstrates that the dissociation constant for NO binding canbe significantly changed by mutating one or more residues in H-NOXproteins. Additionally, the ability of allosteric regulators todramatically affect the dissociation constant and dissociation rate ofNO for sGC supports the ability of mutations that alter the structure ofsGC or other H-NOX proteins to alter the dissociation constant anddissociation rate of NO. If desired, the dissociation constant for NObinding can be further altered by combining any of the mutations listedin Table 4 or by introducing one or more additional mutations into anH-NOX protein, as described herein.

TABLE 4 K_(D) values for NO binding to H—NOX and other hemoproteinsk_(on) k_(off) K_(D) (pM) Hemoprotein (μM⁻¹ s⁻¹) (s⁻¹) 37° C.^(a) sGC>140^(b)  0.001 to 0.66^(c, d) 0.71 to 4710 β1 (1-385)  710^(b)  0.0023to 0.0087^(c, d) 3.24 to 12.3 Hb (T)  18^(e, f) 0.004^(e, f)  411^(g)(222) Hb (R)  18^(e, f) 0.00005^(e, f) 5.14^(g) (2.28) Mb  17^(e, h)0.00012^(e, h) 13.1^(g) (7.06) Tt H—NOX I 0.00056^(j) 0.78 Tt H—NOX I0.00013^(j) 0.18 Y140L L1 H—NOX I 0.00103 to 0.0087^(j) 1.45 to 12.3 L2H—NOX I 0.00036 to 0.00218^(j) 0.51 to 3.1 L2 H—NOX I 0.00051^(j) 0.72F142Y ^(a)calculated from the ratio k_(off):k_(on); ^(b)Zhao, et. al.,(1999). “A Molecular Basis for Nitric Oxide Sensing by Soluble GuanylateCyclase,” PNAS. 96: 14753-14758, measured at 4° C., rates approach rateof diffusion and do not increase significantly at 37° C.; ^(c)Winger, J.A. et al., (January 2007) “Dissociation of Nitric Oxide from SolubleGuanylate Cyclase and Heme-Nitric Oxide/Oxygen Binding DomainConstructs” J. Biol.Chem. 282(2): 897-907; ^(d)k values bracket broadestranges of fits from NO dissociation from 5-coordinate and 6-coordinate,each averaged from 2-4 dissociation experiments using saturating CO and30 mM Na₂S₂O₄ as the NO trap and containing 0.88-2.2 μM protein. Datawere best fit by a double exponential equation: ΔA_(t) = ΔA₁(1 − e^(−k)₁ ^(t)) + ΔA₂(1 − e^(−k) ² ^(t)); ^(e)measured at 20° C.; ^(f)Morris,et. al., 1980 J Biol. Chem. 255: 8050-8053; ^(g)K_(D) calculation,adjusted to 37° C., assuming rate-doubling every 10° C., value at 20° C.shown in brackets; ^(h)Moore, et. al., (1976). “Cooperativity in theDissociation of Nitric Oxide from Hemoglobin,” J Biol. Chem. 251:2788-2794; ^(i)assuming the same k_(on) as β1(1-385) (710 μM⁻¹s⁻¹);^(j)Boon, E. M. et al., (August 2006), “Nitric Oxide Binding toProkaryotic Homologs of the Solube Guanylate Cyclase β1 H0NOX Domain,”J. Biol. Chem. 281(31): 21892-21902.

Table 5 demonstrates that the dissociation rate (k_(off)) for NO bindingcan be significantly changed by mutating one or more residues in H-NOXproteins. The k_(off) for these exemplary mutant H-NOX proteins rangefrom 0.00013 to 0.011 s⁻¹ at 37° C. For Table 5, NO dissociation ratesfrom hemoproteins are derived using chemical traps as indicated in eachcited reference. For comparison, NO dissociation rates from organicnitrates and NONOates are measured using a NO electrode and confirmedusing an oxyhemoglobin trap. Where necessary, values are adjusted to 37°C. using the fact that rates double approximately for every 10° C. Ifdesired, the k_(off) for NO binding can be further altered by combiningany of the single or double mutations listed in Table 5 or byintroducing one or more additional mutations into an H-NOX protein, asdescribed herein.

TABLE 5 Comparison of hemoprotein and nitrovasodilator NO dissociationrates at 37° C. Hemoprotein or Nitrovasodilator k_(off) (s⁻¹) sGC 0.001to 0.66^(a)  β1 (1-385) 0.0023 to 0.0087^(a) β2 (1-217) 0.0069 to0.011^(a)  β1 (1-194) 0.0009 to 0.0041^(a) Tt H—NOX 0.00056^(b) Tt H—NOXY140L 0.00013^(b) Tt H—NOX Y140F 2.0 ± 0.3 × 10^(−4g) L1 H—NOX 0.00103to 0.0087^(b)  L2 H—NOX 0.00036 to 0.00218^(b) L2 H—NOX F142Y0.00051^(b) Hb (T) 0.004^(c) Hb (R) 0.00005^(c) Mb 0.00012^(d)Nitrophorin (pH 5.0) 0.02 to 21^(e) Nitrophorin (pH 8.0) 0.6 to 15^(e) DEA/NO 0.0083^(f) nPRONO 0.00012^(f) ClCH2CH2ONO 0.000022^(f) tBuONO0.000008^(f) ^(a)Winger, J. A. et al., (January 2007) “Dissociation ofNitric Oxide from Soluble Guanylate Cyclase and Heme-Nitric Oxide/OxygenBinding Domain Constructs” J. Biol. Chem. 282(2): 897-907; ^(b)Boon, E.M. et al., (August 2006), “Nitric Oxide Binding to Prokaryotic Homologsof the Solube Guanylate Cyclase β1 H0NOX Domain,” J. Biol. Chem.281(31): 21892-21902; ^(c)Morris, et. al., (1980). “The role ofdiffusion in limiting the rate of ligand binding to hemoglobin” J Biol.Chem. 255: 8050-8053; ^(d)Moore, et. al., (1976). “Cooperativity in thedissociation of nitric oxide from hemoglobin,” J Biol. Chem. 251:2788-2794; ^(e)Maes, et. al., (2004) “Role of Binding Site Loops inControlling Nitric Oxide Release: Structure and Kinetics of Mutant Formsof Nitrophorin 4” Biochemistry 43(21): 6679-90; ^(f)Artz, J. D. et. al.,(1998) “NO Release from NO Donors and Nitrovasodilators: Comparisonsbetween Oxyhemoglobin and Potentiometric Assays,” Chem. Res. Toxicol.11(12): 1393-1397; ^(g)Boon, E. M et al., (2006) “Sensitive andSelective Detection of Nitric Oxide Using an H-NOX Domain,” JACS 128:10022-10023.

As shown in Table 6, introducing one or more mutations into wild-typeH-NOX proteins allows the autoxidation rate and O₂ dissociation rate tobe altered. If desired, the autoxidation rate or O₂ dissociation ratecan be further altered by combining any of the single or doublemutations listed in Table 6 or by introducing one or more additionalmutations into an H-NOX protein, as described herein.

TABLE 6 Stability to autoxidation, O₂-binding properties (such as rateof O₂ dissociation) and distal pocket H-bonding residues are listed forwild-type and class II mutant H—NOX proteins Protein StabilityO₂-binding activity^(b) Distal pocket residues Tt H—NOX, a prokaryoticH—NOX and a strong O₂ binder Tt H—NOX k_(ox) ~ 0^(c) k_(off) = 1.22Trp9, Phe78, Tyr140 Tt Y140F k_(ox) = 0.05 k_(off) = 15.7^(d) Trp9,Phe78, Phe140 Tt Y140L k_(ox) = 0.19 k_(off) = 20.^(d) Trp9, Phe78,Leu140 Tt Y140H k_(ox) = 0.87 k_(off) = 5.03 Trp9, Phe78, His140 TtY140A Stable^(a) Partial complex^(d,e) Trp9, Phe78, Ala140 Tt W9F k_(ox)~ 0^(c) k_(off) = 1.84 Phe9, Phe78, Tyr140 Tt W9F-Y140L k_(ox) = 0.12 Nocomplex formed Phe9, Phe78, Leu140 Tt W9F-Y140H k_(ox) = 0.11 k_(off) =23.4 Phe9, Phe78, His140 Tt F78Y-Y140L k_(ox) ~ 0^(c) k_(off) = 0.83Trp9, Tyr78, Leu140 Tt F78Y-Y140F k_(ox) ~ 0^(c) k_(off) = 1.48 Trp9,Tyr78, Phe140 Prokaryotic H—NOX proteins for which the wild-type proteindoes not bind O₂ L2 H—NOX Stable^(a) No complex formed Phe9, Phe78,Phe142 L2 F142Y Stable^(f) k_(off) = 3.68 Phe9, Phe78, Tyr142 L2F9W-F142Y Stable^(f) Binds O₂ ^(e) Trp9, Phe78, Tyr142 L1 H—NOX k_(ox) =0.31 No complex formed Leu9, Leu78, Phe142 L1 F142Y k_(ox) = 1.8 k_(off)= 1.73^(d) Leu9, Leu78, Tyr142 Eukaryotic H—NOX for which the wild-typeprotein does not bind O₂ β2(1-217) k_(ox) = 0.18 No complex formed Leu9,Cys76, Ile142 β2(1-217) I142Y g Leu9, Cys76, Tyr142 β1(1-194) k_(ox) =4.3 No complex formed Leu9, Cys78, Ile145 β1(1-194) I145Y k_(ox) = 2.8 gLeu9, Cys78, Tyr145 β1(1-194) L9W-I145Y k_(ox) ~ 10 g Trp9, Cys78,Tyr145 β1(1-385) Stable^(e) No complex found Leu9, Cys78, Ile145β1(1-385) I145Y k_(ox) = 0.72 k_(off) = 2.69 Leu9, Cys78, Tyr145β1(1-385) I145H Leu9, Cys78, His145 β1(1-385) C78Y Leu9, Tyr78, Ile145Other H—NOX predicted to bind O₂ as the wild-type construct DdH—NOX(728-899) k_(ox) = 0.98 k_(off) = 5.80 Phe9, Phe75, Tyr139 Dd Y139LPhe9, Phe75, Leu139 Cb H-NOX(1-175) Not stable construct^(h) g Trp9,Phe78, Tyr140 Cb H-NOX(1-186) Slightly more stable^(i) g Trp9, Phe78,Tyr140 Ca H-NOX(1-197) Not stable construct^(h) g Trp9, Phe78, Tyr140 CaH-NOX(1-183) Slightly more stable^(i) g Trp9, Phe78, Tyr140 CeGCY-35(1-252) Stable Binds O₂ ^(e) Phe9, Thr78, Tyr144 ^(a)The constructis stable to oxidation (evaluated by the rate of autoxidation, k_(ox)[h⁻¹] at 37° C.) and/or heme loss. ^(b)O₂-binding activity was evaluatedby the rate of O₂ dissociation from the heme at 20° C. (s⁻¹). ^(c)After24 hours at 37° C., there is still no indication of autoxidation.^(d)Only a small portion of the protein forms a complex with O₂, therate reported represents the kinetics for this population. ^(e)Theprotein binds O₂ but the k_(off) was not determined. ^(f)Althoughrelatively stable, this protein precipitated as it oxidized, making itdifficult to measure k_(ox). ^(g)Not applicable due to instability orrapid oxidation. ^(h)“Not stable construct” means the protein oxidizesimmediately under the conditions tested. ^(i)“Slightly more stable”means the protein oxidizes over a period of minutes to hours, but doesnot remain stable beyond 24 hours under the conditions tested.

Table 7 illustrates the alteration of the O₂ association rate (k_(on)),O₂ dissociation rate (k_(off)), O₂ dissociation constant (K_(D)), andautoxidation rate (k_(ox)) in H-NOX proteins by the introduction of oneor more mutations. In some embodiments, any of the single or doublemutations listed in Table 7 are combined with another mutation (such asanother mutation in Table 7 or any other mutation described herein) tofurther alter the O₂ association rate, O₂ dissociation rate, O₂dissociation constant, autoxidation rate, or combinations of two or moreof the foregoing.

TABLE 7 O₂-binding kinetic constants for histidyl-ligated Fe^(II) hemeproteins Protein K_(D) ^(a) k_(on) ^(b) k_(off) ^(c) k_(ox) ^(d) Ref. TtH—NOX 89.7 ± 6.2  13.6 ± 1.0  1.22 ± 0.09 e I Tt P115A 21.2 ± 2.1  10.4± 1.1  0.22 ± 0.01 e J Tt I5A ~80 0.82 ± 0.03 0.7 J Tt I5L ~1000 9.50 ±0.64 0.6 J Tt I5L-P115A ~30 0.28 ± 0.01 0.6 J Tt W9F 305 ± 31  6.02 ±0.62 1.84 ± 0.17 e I Tt Y140F f 15.7 ± 1.4  15.7 ± 9.8  0.05 J Tt Y140L~2000 Geminal 20.1 ± 2.0  0.19 I Tt Y140H ~500 5.03 ± 0.69 0.87 J TtW9F- ~2500 23.4 ± 3.7  0.11 J Y140H Tt W9F-Y140L No complex with O₂observed 0.12 I Tt F78Y- ~150 1.48 ± 0.33 e J Y140F Tt F78Y- ~80 0.83 ±0.17 e I Y140L Tt W9F-N74A Millimolar very slow J Dd H—NOX Millimolarvery slow 7.13 ± 0.45 0.14 J Dd Y139L No complex with O₂ observed jβ1(1-385) 70,000,00 0.00004 2.69 ± 0.61 0.72 i I145Y L2 F142Y 9200 ±3000 0.40 ± 0.14 3.68 ± 0.71 i Hs Hb beta 267 60 16 n Hs Hb alpha 560 5028 k Sw Mb 880 17 15 0.006 k Bj FixL 140,000 0.14 20 2.7 l HemAT-B 72032 23 0.06 m ^(a)dissociation constant at 20° C. (nM); ^(b)rate of O₂association to the heme at 20° C. (μM⁻¹s⁻¹); ^(c)rate of O₂ dissociationfrom the heme at 20° C. (s⁻¹); ^(d)rate of heme autoxidation (h⁻¹) at37° C.; e after 24 hours at 37° C., still no indication of autoxidation;f only a small portion of the protein forms a complex with O₂, althoughthe kinetics for this population could be measured; i Boon, E. M. et al.(June 2005). “Molecular Basis For NO Selectivity in Soluble GuanylateCyclase,” Nature Chemical Biology 1(1): 53-59, j unpublished data; kSpringer, B. A. et al. (1994) “Family Physicians Key Partners inPreventing Suicide Among Youth,” Chem. Rev. 94: 699-714; lGilles-Gonzalez et al. (1994) “Heme-Based Sensors, Exemplified by theKinase FixL, are a New Class of Heme Protein with Distinctive LigandBinding and Autoxidation,” Biochemistry 33: 8067-8073. m Aono, S. et al.(2002) “Resonance Raman and Ligand Binding Studies of the Oxygen-SensingSignal Transducer Protein HemAT from Bacillus Subtilis,” J. Biol. Chem.277: 13528-13538. n Antonini, E. et al. (1971). “Hemoglobin andMyoglobin in Their Reactions with Ligands,” North-Holland Publ.,Amsterdam.

Table 8 illustrates that the O₂ association rate, O₂ dissociation rate,O₂, autoxidation rate, NO reactivity, and stability of Fe^(II−)O₂complexes in H-NOX proteins may be altered by the introduction of one ormore mutations. In some embodiments, any of the single or doublemutations listed in Table 8 are combined with another mutation (such asanother mutation in Table 8 or any other mutation described herein) tofurther alter the O₂ association rate, O₂ dissociation rate, O₂,autoxidation rate, NO reactivity, or stability of Fe^(II−)O₂ complexesin an H-NOX protein. As will be appreciated by the skilled artisan,introduction of one or more additional mutations, such as thosedescribed herein, may be used to further alter these values.

TABLE 8 O₂ association rate, O₂ dissociation rate, O₂, autoxidationrate, NO reactivity, and stability of Fe^(II)—O₂ complexes in H—NOXproteins. stability of FeII—O₂ Protein k_(on) ^(a) K_(off) ^(b) k_(ox)^(c) NO reactivity^(d) complex Hs Hb 23 11 0.006 <0.001 s oxidizes o/nin air (~7,000 s⁻¹)^(e) at RT, stable at 4° C. in air, stable anaerobicTt H—NOX 13.6 1.22 Very 0.54 ± 0.07 s⁻¹ always stable slow Tt Y140H ~105.03 0.87  1.7 ± 0.4 s⁻¹ oxidizes o/n in air at RT, stable at 4° C. inair, stable anaerobic β1(1-385) ~105 2.69 0.72 slow to Fe^(III)—NOoxidizes o/n in I145Y air at RT, stable at 4° C. in air, stableanaerobic ^(a)rate of O₂ association to the heme at 20° C. (μM−1s−1);^(b)rate of O₂ dissociation from the heme at 20° C. (s−1); ^(c)rate ofheme autoxidation (h−1) at 37° C.; ^(d)For determination of NOreactivities: purified proteins (Tt WT HNOX, Tt Y140H HNOX, Homo sapienshemoglobin (Hs Hb)) were prepared at 2 μM in buffer A and nitric oxide(NO) was prepared at 200 μM in Buffer A (Buffer A: 50 mM Hepes, pH 7.5,50 mM NaCl) at 20° C. Using stopped flow spectroscopy, the protein wasrapidly mixed with NO in a 1:1 ratio with an integration time of 0.00125seconds. The wavelengths of maximum change were fit to a singleexponential, essentially measuring the rate-limiting step of oxidationby NO. The end products of the reaction were ferric-NO for the HNOXproteins and ferric-aquo for Hs Hb. ^(e)For Hs Hb, the reaction of theprotein with NO was so fast that the reaction was completed within thedead time of the experiment (0.001 seconds). The NO reactivity forhemoglobin is approximately 7,000 s⁻¹ at 20° C. based on Eich, R. F. etal. (1996) “Mechanism of NO-Induced Oxidation of Myoglobin andHemoglobin,” Biochemistry 35: 6976-6983.

Table 9 demonstrates that the dissociation constant for O₂ binding canbe significantly changed by mutating one or more residues in H-NOXproteins. The kinetic K_(D) values for these exemplary H-NOX proteinsrange from 21.20 nM to 1000000.00 nM at 20° C. If desired, thedissociation constant for O₂ binding can be further altered by combiningany of the single or double mutations listed in Table 9 or byintroducing one or more additional mutations into an H-NOX protein, asdescribed herein.

TABLE 9 Wild-type and mutant H—NOX proteins and reference proteinsarranged by the value of the dissociation constant for O₂ bindingKinetic K_(D) Calculated K_(D) Protein (nM) ± (nM) Tt P115A 21.2 2.1 TtN74H 27 Tt I5L-P115A 30 Tt N74A 32 Tt I5A 80 Tt F78Y-Y140L 80 Tt H—NOXHis6 89 Tt H—NOX 89.7 6.2 Tt wt 90 Tt F78Y-Y140F 150 Tt W9Y 218 Tt R135QHis6 252 Hs Hb beta 267 Tt W9F 305 31 Tt W9H 456 Tt Y140H 500 Hs Hbalpha 560 Tt W9N 573 Tt I75F-His6 713-773 HemAT-B 720 Sw Mb 880 Tt I5L1000 Tt L144F-His6 1092-1185 Tt Y140L 2000 Tt W9F-Y140H 2500 L2 F142Y9200 3000 Bj FixL 140000 Tt W9F-N74A 1000000 Dd H—NOX 1000000 β1(1-385)I145Y 1000000

Table 10 demonstrates that the dissociation rates for O₂ binding can besignificantly changed by mutating one or more residues in H-NOXproteins. The dissociation rates for these exemplary H-NOX proteinsrange from 0.21 s⁻¹ to 23.4 s⁻¹ at 20° C. If desired, the dissociationrate for O₂ binding can be further altered by combining any of thesingle or double mutations listed in Table 10 or by introducing one ormore additional mutations into an H-NOX protein, as described herein.

TABLE 10 Wild-type and mutant H—NOX proteins and reference proteinsarranged by the value of the dissociation rate for O₂ binding Proteink_(off) (s⁻¹) ± Tt N74A 0.21 0.004 Tt P115A 0.22 0.01 Tt I5L-P115A 0.280.03 Tt N74E 0.38 0.01 Tt N74H 0.44 0.01 Tt I5A 0.82 0.03 Tt F78Y- 0.830.17 Y140L Tt H—NOX His6 1.2 0.02 Tt H—NOX 1.22 0.09 Tt F78Y-Y140F 1.480.33 L1 F142Y 1.73 Tt W9F 1.84 0.17 β1(1-385) 2.69 0.61 I145Y Tt W9Y3.07 0.1 Tt R135Q His6 3.56 0.08 L2 F142Y 3.68 0.71 Tt Y140H 5.03 0.69Tt W9H 6.42 0.11 Dd H—NOX 7.13 0.45 Tt W9N 8.09 0.14 Tt I5L 9.5 0.64 TtI75F-His6 10.48 0.12 Sw Mb 15 Tt Y140F 15.7 9.8 Hs Hb beta 16 TtL144F-His6 16.06 0.21 Bj FixL 20 Tt Y140L 20.1 2 HemAT-B 23 Tt W9F-Y140H23.4 3.7 Hs Hb alpha 28

Table 11 demonstrates that the association rates for O₂ binding can besignificantly changed by mutating one or more residues in H-NOXproteins. The association rates for these exemplary H-NOX proteins rangefrom 60 μM⁻¹s⁻¹ to 0.14 μM⁻¹s⁻¹ at 20° C. If desired, the associationrate for O₂ binding can be further altered by combining any of thesingle or double mutations listed in Table 11 or by introducing one ormore additional mutations into an H-NOX protein, as described herein.

TABLE 11 Wild-type and mutant H—NOX proteins and reference proteinsarranged by the value of the association rate for O₂ binding Proteink_(on) (μM⁻¹s⁻¹) ± Hs Hb beta 60 Hs Hb alpha 50 HemAT-B 32 Sw Mb 17 TtY140F 15.7 1.4 Tt H-NOX 13.6 1 Tt P115A 10.4 1.1 Tt W9F 6.02 0.62 L2F142Y 0.4 0.14 Bj FixL 0.14 Tr W9F-N74A very slow^(a) Dd H—NOX veryslow^(a) β1(1-385) I145Y very slow^(a) ^(a)By “very slow” is meantslower than hemoglobin, such as approximately one to two orders ofmagnitude slower than hemoglobin.

Table 12 illustrates the effect of exemplary H-NOX mutations on NO andO₂-binding. Each number listed in Table 12 for the Fe-unligated form isfor a single peak (which is listed in between the β and α columns). WhenNO or O₂ binds, this single peak splits into two peaks, β and α (whichare listed below the β and α columns, respectively). If desired, NO orO₂-binding can be further altered by combining any of the single ordouble mutations listed in Table 12 or by introducing one or moreadditional mutations into an H-NOX protein, as described herein.

TABLE 12 UV-visible peak positions^(a) for some histidyl-ligated Fe^(II)heme protein complexes Protein Soret β α Fe^(II) unligated complex sGC431 555 β1(1-385) I145Y 429 549 Tt H—NOX 431 565 Tt W9F-Y140L 430 560 VcH—NOX 429 568 Np H—NOX 430 555 L2 H—NOX 428 557 L2 F142Y 428 557 TtI75F-His6 431 569 Tt L144F-His6 433 564 Hb 430 555 Fe^(II)—NO complexsGC 398 537 572 β1(1-385) I145Y 399/416 542 574 Tt H—NOX 420 547 575 TtW9F-Y140L 423 540 573 Vc H—NOX 398 540 573 Np H—NOX 416/400 543 576 L2H—NOX 399/416 544 575 L2 F142Y 417 544 578 Tt I75F-His6 418 545 574 TtL144F-His6 416 544 574 Hb 418 545 575 Fe^(II)—O₂ complex sGC No complexobserved β1(1-385) I145Y 416 541 575 Tt H—NOX 416 556 591 Tt W9F-Y140LNo complex observed Vc H—NOX No complex observed Np H—NOX No complexobserved L2 H—NOX No complex observed L2 F142Y 417 542 577 Tt I75F-His6416 552 589 Tt L144F-His6 416 544 574 Hb 415 541 577 ^(a)nm (at 20° C.)

Table 13 contains UV-visible peak positions for some Fe (II), Fe (III),Fe(II)-NO, and Fe(II)-O₂ complexes. When a hemoglobin or H-NOX proteinis anaerobic, it has a Soret peak at ˜431 nm, and it is in an unligatedstate. If the H-NOX protein does not bind NO, then the Soret peak willnot change when NO is added. If the H-NOX protein binds NO and forms a6-coordinate ferrous-nitrosyl complex, then its Soret peak will shift tobetween 420 nm and 424 nm when NO is added. If the H-NOX protein bindsNO and forms a 5-coordinate ferrous-nitrosyl complex, the Soret peakwill shift to ˜399 nm. If the H-NOX protein does not bind O₂, then theSoret peak will not change when O₂ is added. If the H-NOX protein doesbind O₂, then its Soret peak will shift to between 414 nm and 418 nmwhen O₂ is added, which is the same shift that occurs in hemoglobin,indicative of O₂ bound to the heme. Soret peaks for oxidized H-NOX(Fe(III)) may be relevant to the state of the H-NOX protein afterstorage or use. If desired, NO or O₂-binding can be further altered bycombining any of the single or double mutations listed in Table 13 or byintroducing one or more additional mutations into an H-NOX protein, asdescribed herein.

TABLE 13 UV-visible peak positions for some Fe (II), Fe (III),Fe(II)—NO, and Fe(II)—O₂ complexes. Complex Protein Soret β α Fe (II) Ttwt 430 563 Tt W9Y 430 569 Tt N74A 433 558 Tt N74H 431 561 Tt N74A-Y140H430 567 Tt W9H 431 563 Tt N74E 433 559 Tt W9N 431 569 Tt wt His₆ 430 565Complex Protein Soret β^(α) α Fe (III) Tt wt 413 550 585 Tt W9Y 409 N.A.Tt N74A 416 554 586 Tt N74H 408 N.A. Tt N74A-Y140H 407 N.A. Tt W9H 407N.A. Tt N74E 408 N.A. Tt W9N 408 N.A. Tt wt His₆ 413 550 586 ComplexProtein Soret β α Fe(II)—NO Tt wt 420 550 578 Tt W9Y 420 552 576 Tt N74A421 572 Tt N74H 424 562 Tt N74A-Y140H 421 549 576 Tt W9H 420 548 575 TtN74E 422 544 571 Tt W9N 421 541 576 Tt wt His₆ 420 547 576 ComplexProtein Soret β α Fe(II)—O₂ Tt wt 416 556 591 Tt W 9Y 416 555 590 TtN74A 418 553 589 Tt N74H 418 553 589 Tt N74A-Y140H 414 555 584 Tt W9H418 556 589 Tt N74E 417 555 587 Tt W9N 416 588 553 Tt wt His₆ 416 556591 ^(a)“N.A.” denotes nonassignable α and β bands due to low signal atlonger wavelengths.

Table 14 contains autoxidation rates for exemplary T. tengcongensisH-NOX proteins. If desired, the autoxidation rate can be further alteredby combining any of the mutations listed in Table 14 or by introducingone or more additional mutations into an H-NOX protein, as describedherein. The 2 nm and 3 nm values mean in Table 14 refer to a shift inthe UV-Vis Soret peak by 2 to 3 nm over the time period of theobservation; this extremely small change may be due to autoxidation.

TABLE 14 Autoxidation rates for T. tengcongensis (Tt) H-NOX proteinsAutoxidation Rate Protein (25° C., hr⁻¹)^(a) Tt wt Stable Tt W9Y StableTt N74A Stable Tt N74H stable at 4° C., very slow at RT (2 nm) Tt W9HStable Tt N74E very slow at 4° C. (2 nm), slow at RT Tt W9N stable at 4°C., very slow at RT (3 nm) Tt wt His₆ Stable Tt I75F-His6 Stable TtL144F-His6 Stable ^(a)“Stable” denotes lack of heme oxidation after atleast 24 hours. “RT” denotes room temperature.H-NOX Nucleic Acids

The invention also features nucleic acids encoding any of the mutantH-NOX proteins described herein. As used herein, a “nucleic acid” refersto two or more deoxyribonucleotides and/or ribonucleotides in eithersingle or double-stranded form, and unless otherwise limited,encompasses known analogs of naturally-occurring nucleotides thathybridize to nucleic acids in a manner similar to nucleotides occurringin nature. In some embodiments, the nucleic acid is a recombinantnucleic acid. By “recombinant nucleic acid” means a nucleic acid ofinterest that is free of one or more nucleic acids (e.g., genes) which,in the genome occurring in nature of the organism from which the nucleicacid of interest is derived, flank the nucleic acid of interest. In someembodiments, an H-NOX nucleic acid is operably linked to another nucleicacid encoding all or a portion of another protein such that therecombinant nucleic acid encodes a fusion protein that includes an H-NOXprotein (e.g., an H-NOX domain with or without another domain from anH-NOX protein) and all or part of another protein, such as human serumalbumin. The term therefore includes, for example, a recombinant DNAwhich is incorporated into a vector, into an autonomously replicatingplasmid or virus, or into the genomic DNA of a prokaryote or eukaryote,or which exists as a separate molecule (e.g., a cDNA, a genomic DNAfragment, or a cDNA fragment produced by PCR or restriction endonucleasedigestion) independent of other sequences.

The invention also features vectors with one more nucleic acids encodingany of the mutant H-NOX proteins that are described herein. As usedherein, a “vector” means a construct that is capable of delivering, andoptionally expressing one or more nucleic acids of interest in a hostcell. Examples of vectors include, but are not limited to, plasmids,viral vectors, DNA or RNA expression vectors, cosmids, and phagevectors. In some embodiments, the vector contains a nucleic acid underthe control of an expression control sequence. An “expression controlsequence” means a nucleic acid sequence that directs transcription of anucleic acid of interest. An expression control sequence can be apromoter, such as a constitutive or an inducible promoter, or anenhancer. The expression control sequence is operably linked to thenucleic acid segment to be transcribed.

In particular embodiments, the nucleic acid includes a segment of or theentire nucleic acid sequence of any of the nucleic acids shown in FIG.2-4D or 8A-8DD. In some embodiments, the nucleic acid includes at leastabout 50, 100, 150, 200, 300, 400, 500, 600, 700, 800, or morecontiguous nucleotides from a H-NOX nucleic acid and contains one ormore mutations (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 mutations)compared to the H-NOX nucleic acid from which it was derived. In variousembodiments, a mutant H-NOX nucleic acid contains less than about 20,15, 12, 10, 9, 8, 7, 6, 5, 4, 3, or 2 mutations compared to the H-NOXnucleic acid from which it was derived. The invention also featuresdegenerate variants of any nucleic acid encoding a mutant H-NOX protein.

The invention also includes a cell or population of cells containing atleast one nucleic acid encoding a mutant H-NOX protein described herein.Exemplary cells include insect, plant, yeast, bacterial, and mammaliancells. These cells are useful for the production of mutant H-NOXproteins using standard methods, such as those described herein.

Formulations of H-NOX Proteins

Any wild-type or mutant H-NOX protein described herein may be used forthe formulation of pharmaceutical or non-pharmaceutical compositions. Asdiscussed further below, these formulations are useful in a variety oftherapeutic and industrial applications.

In some embodiments, the pharmaceutical composition includes one or morewild-type or mutant H-NOX proteins (such as any of the H-NOX wild-typeor mutant proteins described herein) and a pharmaceutically acceptablecarrier. In various embodiments, the H-NOX protein is an isolated orpurified protein. By “pharmaceutically acceptable carrier” is meant anymaterial which, when combined with an active ingredient, allows theingredient to retain biological activity and does not provoke anunacceptable immune response (e.g., a severe allergy or anaphylacticshock) based on the knowledge of a skilled practitioner. Examplesinclude, but are not limited to, any of the standard pharmaceuticalcarriers such as phosphate buffered saline solutions, water, emulsionssuch as oil/water emulsion, and various types of wetting agents.Exemplary diluents for aerosol or parenteral administration arephosphate buffered saline or normal (0.9%) saline. Compositionscomprising such carriers are formulated by well known conventionalmethods (see, for example, Remington's Pharmaceutical Sciences, 18thedition, A. Gennaro, ed., Mack Publishing Co., Easton, Pa., 1990; andRemington, The Science and Practice of Pharmacy 20th Ed. MackPublishing, 2000, which are each hereby incorporated by reference intheir entireties, particularly with respect to formulations).

While any suitable carrier known to those of ordinary skill in the artmay be employed in the pharmaceutical compositions of this invention,the type of carrier will vary depending on the mode of administration.Compositions can be formulated for any appropriate manner ofadministration, including, for example, intravenous, intra-arterial,intravesicular, inhalation, intraperitoneal, intrapulmonary,intramuscular, subcutaneous, intra-tracheal, transmucosal, intraocular,intrathecal, or transdermal administration. For parenteraladministration, such as subcutaneous injection, the carrier may include,e.g., water, saline, alcohol, a fat, a wax, or a buffer. For oraladministration, any of the above carriers or a solid carrier, such asmannitol, lactose, starch, magnesium stearate, sodium saccharine,talcum, cellulose, glucose, sucrose, or magnesium carbonate, may beemployed. Biodegradable microspheres (e.g., polylactate polyglycolate)may also be used as carriers.

In some embodiments, the pharmaceutical or non-pharmaceuticalcompositions include a buffer (e.g., neutral buffered saline, phosphatebuffered saline, etc), a carbohydrate (e.g., glucose, mannose, sucrose,dextran, etc), an antioxidant, a chelating agent (e.g., EDTA,glutathione, etc.), a preservative, another compound useful for bindingand/or transporting NO, an inactive ingredient (e.g., a stabilizer,filler, etc), or combinations of two or more of the foregoing. In someembodiments, the composition is formulated as a lyophilizate. H-NOXproteins may also be encapsulated within liposomes or nanoparticlesusing well known technology. Other exemplary formulations that can beused for H-NOX proteins are described by, e.g., U.S. Pat. Nos.6,974,795, and 6,432,918, which are each hereby incorporated byreference in their entireties, particularly with respect to formulationsof proteins.

The compositions described herein may be administered as part of asustained release formulation (e.g., a formulation such as a capsule orsponge that produces a slow release of compound followingadministration). Such formulations may generally be prepared using wellknown technology and administered by, for example, oral, rectal orsubcutaneous implantation, or by implantation at the desired targetsite. Sustained-release formulations may contain an H-NOX proteindispersed in a carrier matrix and/or contained within a reservoirsurrounded by a rate controlling membrane. Carriers for use within suchformulations are biocompatible, and may also be biodegradable. In someembodiments, the formulation provides a relatively constant level ofH-NOX protein release. The amount of H-NOX protein contained within asustained release formulation depends upon the site of implantation, therate and expected duration of release, and the nature of the conditionto be treated or prevented.

In some embodiments, the pharmaceutical composition contains aneffective amount of a wild-type or mutant H-NOX protein. The term“effective amount” intends such amount of one or more proteins describedherein which in combination with its parameters of efficacy and toxicityshould be effective in a given therapeutic form based on the knowledgeof the practicing specialist. As is understood in the art, an effectiveamount can be in one or more doses. As is understood in the clinicalcontext, an effective dosage of a pharmaceutical composition may or maynot be achieved in conjunction with another drug, compound, orpharmaceutical composition. Thus, an effective amount can be consideredin the context of administering one or more therapeutic agents, and asingle agent can be considered to be given in an effective amount if, inconjunction with one or more other agents, a desirable or beneficialresult can be or is achieved.

An exemplary dose of hemoglobin as a blood substitute is from about 10mg to about 5 grams or more of extracellular hemoglobin per kilogram ofpatient body weight. Similar doses of H-NOX proteins can be use for thedelivery of NO. Thus, in some embodiments, an effective amount of anH-NOX protein for administration to a human is between a few grams toover about 350 grams. Other exemplary doses of an H-NOX protein includeabout any of 4.4, 5, 10, or 13 G/DL (where G/DL is the concentration ofthe H-NOX protein solution prior to infusion into the circulation) at anappropriate infusion rate, such as about 0.5 ml/min (see, for example,Winslow, R. Chapter 12 In Blood Substitutes). In some embodiments, adose of less than 10 mg of H-NOX protein is used for temporaryvasodilation. It will be appreciated that the unit content of activeingredients contained in an individual dose of each dosage form need notin itself constitute an effective amount since the necessary effectiveamount could be reached by the combined effect of a plurality ofadministrations. The selection of the amount of an H-NOX protein toinclude in a pharmaceutical composition depends upon the dosage formutilized, the condition being treated, and the particular purpose to beachieved according to the determination of the ordinarily skilledartisan in the field.

Exemplary compositions include genetically engineered, recombinant H-NOXproteins, which may be isolated or purified, comprising one or moremutations that collectively impart altered NO or O₂ ligand-bindingrelative to the corresponding wild-type H-NOX protein, and operative asa physiologically compatible mammalian blood gas NO carrier. Forexample, mutant H-NOX proteins as described herein.

The invention also provides NO carriers comprising or consistingessentially of one or more wild-type or mutant H-NOX proteins. Suitablebuffers and other ingredients for formulating proteins (such as proteinsdelivered to the blood or gastrointestinal system) are known in the art.

To reduce or prevent an immune response in human subjects who areadministered a pharmaceutical composition, human H-NOX proteins (eitherwild-type human proteins or human proteins into which one or moremutations have been introduced) or other non-antigenic H-NOX proteins(e.g., mammalian H-NOX proteins) can be used. To reduce or eliminate theimmunogenicity of H-NOX proteins derived from sources other than humans,amino acids in an H-NOX protein can be mutated to the correspondingamino acids in a human H-NOX. For example, one or more amino acids onthe surface of the tertiary structure of a non-human H-NOX protein canbe mutated to the corresponding amino acid in a human H-NOX protein.

Therapeutic Applications of H-NOX Proteins

Any of the wild-type or mutant H-NOX proteins (e.g., isolated orpurified H-NOX proteins) or pharmaceutical compositions described hereinmay be used in therapeutic applications.

Particular H-NOX Proteins can be Selected for Such Applications Based onthe Desired

NO dissociation constant, O₂ dissociation constant, NO k_(off), O₂k_(off), NO reactivity, NO stability, autoxidation rate, plasmaretention time, half-life, or any combination of two or more of theforegoing for the particular indication being treated. H-NOX proteinscan be used to treat any condition for which delivery of NO isbeneficial. Exemplary target indications include diseases of functionalNO deficiency, such as where a vasodilator or an NO carrier isindicated, including conditions exacerbated by chronic hypertension,such as heart failure, renal failure, and stroke. In variousembodiments, the treated condition is a cardiovascular condition (e.g.,myocardial infarction or heart surgery), hypertension, avasoconstrictive condition (e.g., stroke), erectile dysfunction,constipation, or bowel obstruction. For the treatment of constipation orbowel obstruction, H-NOX proteins can be used to deliver NO to treat asphincter control deficit, thereby relaxing the smooth muscle. Forexample, H-NOX proteins that function in the digestive system can relaxthe smooth muscle of the ileum as the H-NOX proteins pass through thedigestive system. The methods and compositions are applicable to bothacute (providing rapid NO to tissues or a specific site, e.g., acutemyocardial infarction or stroke) and chronic situations (e.g., chronichypertension or post-acute recovery from cardiac infarction or stroke).

In various embodiments, the invention features a method of delivering NOto an individual (e.g., a mammal, such as a primate (e.g., a human, amonkey, a gorilla, an ape, a lemur, etc), a bovine, an equine, aporcine, a canine, or a feline) by administering to an individual inneed thereof a wild-type or mutant H-NOX protein in an amount sufficientto deliver NO to the individual. In some embodiments, the inventionprovides methods of carrying or delivering blood gas to an individualsuch as a mammal, comprising the step of delivering to the blood of theindividual (e.g., a mammal) one or more of H-NOX compositions. Methodsfor delivering proteins to the blood, digestive system, or tissues(e.g., mammalian blood or tissues) are known in the art. In variousembodiments, the H-NOX protein is an apoprotein that is capable ofbinding heme or is a holoprotein with heme bound. The H-NOX protein mayor may not have heme bound prior to the administration of the H-NOXprotein to the individual. In some embodiments, NO is bound to the H-NOXprotein before it is delivered to the individual. In other embodiments,NO is not bound to the H-NOX protein prior to the administration of theprotein to the individual, and the H-NOX protein transports NO from onelocation in the individual to another location in the individual. Forexample, in particular embodiments, H-NOX proteins bind NO in the bloodstream and only release it where NO concentrations are very low (such assites of vasoconstriction). This targeted delivery of NO may producefewer side-effects than conventional vasodilators that release NOindependent of local NO concentration and thus function systemically,with side effects such as headaches and peripheral tingling.

The methods of the present invention can be used to treat anyindividual. For use herein, unless clearly indicated otherwise, “anindividual” as used herein intends a mammal, including but not limitedto, a primate (e.g., a human, monkey, gorilla, ape, lemur, etc.), abovine, an equine, a porcine, a canine, and a feline. Thus, theinvention finds use in both human medicine and in the veterinarycontext, including use in agricultural animals and domestic pets. Theindividual may have been diagnosed with, is suspected of having, or isat risk of developing an indication, such as a cardiovascular condition(e.g., myocardial infarction or heart surgery), hypertension, acondition exacerbated by hypertension (e.g., heart failure, renalfailure, or stroke), a vasoconstrictive condition (e.g., stroke), afunctional NO deficiency, erectile dysfunction, constipation, or bowelobstruction. The individual may exhibit one or more symptoms associatedwith the indication. The individual can be genetically or otherwisepredisposed to developing such a condition.

As used herein, “in need thereof” includes individuals who have acondition or disease (e.g., as a cardiovascular condition such asmyocardial infarction or heart surgery, hypertension, a conditionexacerbated by hypertension such as heart failure, renal failure, orstroke, a vasoconstrictive condition such as stroke, a functional NOdeficiency, erectile dysfunction, constipation, or bowel obstruction) orare “at risk” for the condition or disease. As used herein, an “at risk”individual is an individual who is at risk of development of acondition, such as a cardiovascular condition (e.g., myocardialinfarction or heart surgery), hypertension, a condition exacerbated byhypertension (e.g., heart failure, renal failure, or stroke), avasoconstrictive condition (e.g., stroke), a functional NO deficiency,erectile dysfunction, constipation, or bowel obstruction. An individual“at risk” may or may not have a detectable disease or condition, and mayor may not have displayed detectable disease prior to the treatmentmethods described herein. “At risk” denotes that an individual has oneor more so-called risk factors, which are measurable parameters thatcorrelate with development of a disease or condition and are known inthe art. An individual having one or more of these risk factors has ahigher probability of developing the disease or condition than anindividual without these risk factor(s). These risk factors include, butare not limited to, age, sex, race, diet, history of previous disease,presence of precursor disease, genetic (i.e., hereditary)considerations, and environmental exposure.

These methods can be used to treat or delay any condition for whichdelivery of NO is beneficial. By “treatment” or “treating” is meant anapproach for obtaining a beneficial or desired result, includingclinical results. For purposes of this invention, beneficial or desiredresults include, but are not limited to, alleviation of symptomsassociated with a condition (such as, but not limited to, acardiovascular condition such as myocardial infarction or heart surgery,hypertension, a condition exacerbated by hypertension such as heartfailure, renal failure, or stroke, a vasoconstrictive condition such asstroke, a functional NO deficiency, erectile dysfunction, constipation,or bowel obstruction) diminishment of the extent of the symptomsassociated with a condition, or prevention of a worsening of thesymptoms associated with a condition. In some embodiments, treatmentwith a one or more proteins disclosed herein is accompanied by no orfewer side effects than are associated with currently availabletherapies.

As used herein, “delaying” development of a disease or condition meansto defer, hinder, slow, retard, stabilize and/or postpone development ofthe disease or condition, such as a cardiovascular condition (e.g.,myocardial infarction or heart surgery), hypertension, a conditionexacerbated by hypertension (e.g., heart failure, renal failure, orstroke), a vasoconstrictive condition (e.g., stroke), a functional NOdeficiency, erectile dysfunction, constipation, or bowel obstruction.This delay can be of varying lengths of time, depending on the historyof the disease and/or individual being treated. As is evident to oneskilled in the art, a sufficient or significant delay can, in effect,encompass prevention, in that the individual does not develop thedisease or condition. For example, the method may reduce the probabilityof disease development in a given time frame and/or reduce the extent ofthe disease in a given time frame, when compared to not using themethod. In some embodiments, such comparisons are based on clinicalstudies using a statistically significant number of subjects. Diseasedevelopment can be detectable using standard clinical techniques.Development may also refer to disease progression that can be initiallyundetectable and includes occurrence, recurrence, and onset.

In some embodiments for the direct delivery of an H-NOX protein withbound NO to a particular site in the body (such as a tissue or organ),the k_(off) for NO is more important than the K_(D) because NO isalready bound to the protein (making the k_(on) less important) and NOneeds to be released at or near a particular site in the body (at a rateinfluenced by the K_(off)). In some embodiments for the treatment ofacute conditions, the H-NOX protein has a relatively high k_(off), k₁ ork₂ for NO (such as at least about any of 0.05 s⁻¹, 0.1 s⁻¹, or 1.0 s⁻¹)so that vasodilation occurs rapidly. In some embodiments for systemicadministration, the H-NOX protein has a relatively low k_(off), k₁, ork₂ for NO (such as at less than about any of 0.05 s⁻¹, 0.01 s⁻¹, or0.001 s⁻¹) so that NO is not released until the H-NOX protein reaches asite of low NO concentration (e.g., a vasoconstricted site).

H-NOX proteins can also be used for imaging. In particular, lightimaging (e.g., optical coherence tomography; see, for example, Villard,J. W. (2002). “Use of a Blood Substitute to Determine InstantaneousMurine Right Ventricular Thickening with Optical Coherence Tomography,”Circulation 105:1843-1849, which is incorporated by reference in itsentirety particularly with respect to optical coherence tomography) isobfuscated by erythrocytes. Perfusion with an H-NOX solution allows forclearer images of the circulation and vessel walls because the H-NOXprotein is much smaller than erythrocytes.

H-NOX proteins and pharmaceutical compositions of the invention can beadministered to an individual by any conventional means such as by oral,topical, intraocular, intrathecal, intrapulmonary, intra-tracheal, oraerosol administration; by transdermal or mucus membrane adsorption; orby injection (e.g., subcutaneous, intravenous, intra-arterial,intravesicular, or intramuscular injection). H-NOX proteins may also beincluded in large volume parenteral solutions for administration to theblood. In exemplary embodiments, the H-NOX protein is administered tothe blood (e.g., administration to a blood vessel such as a vein,artery, or capillary) of the individual.

In some embodiments, a sustained continuous release formulation of thecomposition is used. Administration of an H-NOX protein can occur, e.g.,for a period of seconds to hours depending on the purpose of theadministration. For acute conditions, an exemplary time course ofadministration is as rapid as possible. Other exemplary time coursesinclude about 10, 20, 30, 40, 60, 90, or 120 minutes. Exemplary infusionrates for H-NOX solutions are from about 30 mL/hour to about 13,260mL/hour, such as about 100 mL/hour to about 3,000 mL/hour. An exemplarytotal dose of H-NOX protein is about 900 mg/kg administered over 20minutes at 13,260 mL/hour. An exemplary total dose of H-NOX protein fora swine is about 18.9 grams.

Exemplary dosing frequencies include, but are not limited to, at least1, 2, 3, 4, 5, 6, or 7 times (i.e., daily) a week. In some embodiments,an H-NOX protein is administered at least 2, 3, 4, or 6 times a day. TheH-NOX protein can be administered, e.g., over a period of a few days orweeks. In some embodiments, the H-NOX protein is administrated for alonger period, such as a few months or years. The dosing frequency ofthe composition may be adjusted over the course of the treatment basedon the judgment of the administering physician.

As noted above, the selection of dosage amounts for H-NOX proteinsdepends upon the dosage form utilized, the frequency and number ofadministrations, the condition being treated, and the particular purposeto be achieved according to the determination of the ordinarily skilledartisan in the field. In some embodiments, an effective amount of anH-NOX protein for administration to human is between a few grams to over350 grams.

In some embodiments, two or more different H-NOX proteins areadministered simultaneously, sequentially, or concurrently. In someembodiments, another compound or therapy useful for the delivery of NOis administered simultaneously, sequentially, or concurrently with theadministration of one or more H-NOX proteins.

Industrial Applications of H-NOX Proteins

The H-NOX proteins and composition described herein can also be used fora number of in vitro or industrial applications (see, e.g., U.S. Pat.No. 6,455,676, which is hereby incorporated by reference in itsentirety, particularly with respect to in vitro or industrialapplications). Particular H-NOX proteins can be selected for suchapplications based on the desired NO dissociation constant, O₂dissociation constant, NO k_(off), O₂ k_(off), NO reactivity, NOstability, autoxidation rate, half-life, or any combination of two ormore of the foregoing for the particular application. In variousembodiments of industrial applications, the H-NOX protein is anapoprotein that is capable of binding heme or is a holoprotein with hemebound.

H-NOX proteins can be used to add NO to solutions for which NO isdesirable. In embodiments that use bioreactors that require anaerobicfermentation, H-NOX proteins are used to deliver NO delivery to cells.For example, the delivery of NO to mitochondria may limit oxidativephosphorylation and enhance metabolism through the lactate pathway. TheH-NOX protein in Clostridium acetobutylicum, which is cultured underanaerobic fermentation as a biofuel generator, may naturally serve thisfunction. Moreover, the H-NOX proteins can be used to remove NO fromsolutions requiring the removal of NO. For example, H-NOX proteins maybe used to absorb or remove NO in bioreactors where NO is an inhibitorof cellular proliferation and/or mitochondrial function. Removing NO mayimprove mitochondrial function, limit apoptosis, increase per-cellproductivity, or any combination of two or more of the foregoing.

Kits with H-NOX Proteins

Also provided are articles of manufacture and kits that include any ofthe H-NOX proteins described herein and suitable packaging. In someembodiments, the invention includes a kit with (i) an H-NOX protein(such as a wild-type or mutant H-NOX protein described herein orformulations thereof as described herein) and (ii) instructions forusing the kit to deliver NO to an individual. In various embodiments,the invention features a kit with (i) an H-NOX protein (such as awild-type or mutant H-NOX protein described herein or formulationsthereof as described herein) and (ii) instructions for using the kit forany of the industrial uses described herein (e.g., addition of NO to asolution or removal of NO from a solution).

Suitable packaging for compositions described herein are known in theart, and include, for example, vials (e.g., sealed vials), vessels,ampules, bottles, jars, flexible packaging (e.g., sealed Mylar orplastic bags), and the like. These articles of manufacture may furtherbe sterilized and/or sealed. Also provided are unit dosage formscomprising the compositions described herein. These unit dosage formscan be stored in a suitable packaging in single or multiple unit dosagesand may also be further sterilized and sealed. Instructions supplied inthe kits of the invention are typically written instructions on a labelor package insert (e.g., a paper sheet included in the kit), butmachine-readable instructions (e.g., instructions carried on a magneticor optical storage disk) are also acceptable. The instructions relatingto the use of H-NOX proteins generally include information as to dosage,dosing schedule, and route of administration for the intended treatmentor industrial use. The kit may further comprise a description ofselecting an individual suitable or treatment.

The containers may be unit doses, bulk packages (e.g., multi-dosepackages) or sub-unit doses. For example, kits may also be provided thatcontain sufficient dosages of H-NOX proteins disclosed herein to provideeffective treatment for an individual for an extended period, such asabout any of a week, 2 weeks, 3 weeks, 4 weeks, 6 weeks, 8 weeks, 3months, 4 months, 5 months, 6 months, 7 months, 8 months, 9 months, ormore. Kits may also include multiple unit doses of H-NOX proteins andinstructions for use and packaged in quantities sufficient for storageand use in pharmacies, for example, hospital pharmacies and compoundingpharmacies. In some embodiments, the kit includes a dry (e.g.,lyophilized) composition that can be reconstituted, resuspended, orrehydrated to form generally a stable aqueous suspension of H-NOXprotein.

Exemplary Methods for Production of H-NOX Proteins

The present invention also provides methods for the production of any ofthe mutant H-NOX proteins described herein. In some embodiments, themethod involves culturing a cell that has a nucleic acid encoding amutant H-NOX protein under conditions suitable for production of themutant H-NOX protein. In various embodiments, the mutant H-NOX is alsopurified (such as purification of the H-NOX protein from the cells orthe culture medium).

As noted above, the sequences of several wild-type H-NOX proteins andnucleic acids are known and can be use to generate mutant H-NOX proteinsand nucleic acids of the present invention. Techniques for the mutation,expression, and purification of recombinant H-NOX proteins have beendescribed by, e.g., Boon, E. M. et al. (2005). “Molecular Basis For NOSelectivity in Soluble Guanylate Cyclase,” Nature Chemical Biology1:53-59 and Karow, D. S. et al. (Aug. 10, 2004). “SpectroscopicCharacterization of The Soluble Guanylate Cyclase-Like Heme Domains FromVibrio Cholerae And Thermoanaerobacter Tengcongensis,” Biochemistry43(31):10203-10211, which is hereby incorporated by reference in itsentirety, particularly with respect to the mutation, expression, andpurification of recombinant H-NOX proteins. These techniques or otherstandard techniques can be used to generate any mutant H-NOX protein.

In particular, mutant H-NOX proteins described herein can be generated anumber of methods that are known in the art. Mutation can occur ateither the amino acid level by chemical modification of an amino acid orat the codon level by alteration of the nucleotide sequence that codesfor a given amino acid. Substitution of an amino acid at any givenposition in a protein can be achieved by altering the codon that codesfor that amino acid. This can be accomplished by site-directedmutagenesis using, for example: (i) the Amersham technique (Amershammutagenesis kit, Amersham, Inc., Cleveland, Ohio) based on the methodsof Taylor, J. W. et al. (Dec. 20, 1985). “The Use ofPhosphorothioate-Modified DNA in Restriction Enzyme Reactions to PrepareNicked DNA,” Nucleic Acids Res. 13(24):8749-8764; Taylor, J. W. et al.(Dec. 20, 1985). “The Rapid Generation of Oligonucleotide-DirectedMutations at High Frequency Using Phosphorothioate-Modified DNA,”Nucleic Acids Res. 13(24):8765-8785; Nakamaye, K. L. et al. (Dec. 22,1986). “Inhibition of Restriction Endonuclease Nci I Cleavage byPhosphorothioate Groups and its Application to Oligonucleotide-DirectedMutagenesis,” Nucleic Acids Res. 14(24):9679-9698; and Dente et al.(1985). in DNA Cloning, Glover, Ed., IRL Press, pages 791-802, (ii) thePromega kit (Promega Inc., Madison, Wis.), or (iii) the Biorad kit(Biorad Inc., Richmond, Calif.), based on the methods of Kunkel, T. A.(January 1985). “Rapid And Efficient Site-Specific Mutagenesis WithoutPhenotypic Selection,” Proc. Natl. Acad. Sci. USA 82(2):488-492; Kunkel,T. A. (1987). “Rapid And Efficient Site-Specific Mutagenesis WithoutPhenotypic Selection,” Methods Enzymol. 154:367-382; Kunkel, U.S. Pat.No. 4,873,192, which are each hereby incorporated by reference in theirentireties, particularly with respect to the mutagenesis of proteins.Mutagenesis can also be accomplished by other commercially available ornon-commercial means, such as those that utilize site-directedmutagenesis with mutant oligonucleotides.

Site-directed mutagenesis can also be accomplished using PCR-basedmutagenesis such as that described in Zhengbin et al. (1992). pages205-207 in PCR Methods and Applications, Cold Spring Harbor LaboratoryPress, New York; Jones, D. H. et al. (February 1990). “A Rapid MethodFor Site-Specific Mutagenesis And Directional Subcloning by Using thePolymerase Chain Reaction to Generate Recombinant Circles,”Biotechniques 8(2):178-183; Jones, D. H. et al. (January 1991). “A RapidMethod For Recombination And Site-Specific Mutagenesis by PlacingHomologous Ends on DNA Using Polymerase Chain Reaction,” Biotechniques10(1):62-66, which are each hereby incorporated by reference in theirentireties, particularly with respect to the mutagenesis of proteins.Site-directed mutagenesis can also be accomplished using cassettemutagenesis with techniques that are known to those of skill in the art.

A mutant H-NOX nucleic acid can be incorporated into a vector, such asan expression vector, using standard techniques. For example,restriction enzymes can be used to cleave the mutant H-NOX nucleic acidand the vector. Then, the compatible ends of the cleaved mutant H-NOXnucleic acid and the cleaved vector can be ligated. The resulting vectorcan be inserted into a cell (e.g., an insect cell, a plant cell, a yeastcell, or a bacterial cell) using standard techniques (e.g.,electroporation) for expression of the encoded H-NOX protein.

In particular, heterologous proteins have been expressed in a number ofbiological expression systems, such as insect cells, plant cells, yeastcells, and bacterial cells. Thus, any suitable biological proteinexpression system can be utilized to produce large quantities ofrecombinant H-NOX protein. In some embodiments, the H-NOX protein (e.g.,a mutant or wild-type H-NOX protein) is an isolated protein. As usedherein, an “isolated protein” means a protein separated from one or morecomponents with which the protein is naturally associated in nature,including, for example, nucleic acids, lipids, and other proteins. Anisolated protein also does not occur in a library of proteins, such as alibrary of 2, 5, 10, 20, 50 or more different proteins. An isolatedprotein can be obtained, for example, by expression of a recombinantnucleic acid encoding the protein or by chemical synthesis of theprotein.

If desired, H-NOX proteins can be purified using standard techniques. Asused herein, a “purified protein” means a protein (e.g., a mutant orwild-type H-NOX protein) that has been separated from one or morecomponents that are present when the protein is produced. In someembodiments, the protein is at least about 60%, by weight, free fromother components that are present when the protein is produced. Invarious embodiments, the protein is at least about 75%, 90%, or 99%, byweight, pure. A purified protein can be obtained, for example, bypurification (e.g., extraction) from a natural source, a recombinantexpression system, or a reaction mixture for chemical synthesis.Exemplary methods of purification include immunoprecipitation, columnchromatography such as immunoaffinity chromatography, magnetic beadimmunoaffinity purification, and panning with a plate-bound antibody, aswell as other techniques known to the skilled artisan. Purity can beassayed by any appropriate method, e.g., by column chromatography,polyacrylamide gel electrophoresis, or HPLC analysis. In someembodiments, the purified protein is incorporated into a pharmaceuticalcomposition of the invention or used in a method of the invention. Thepharmaceutical composition of the invention may have additives,carriers, or other components in addition to the purified protein.

EXAMPLES

The examples, which are intended to be purely exemplary of the inventionand should therefore not be considered to limit the invention in anyway, also describe and detail aspects and embodiments of the inventiondiscussed above. The examples are not intended to represent that theexperiments below are all or the only experiments performed. Unlessindicated otherwise, temperature is in degrees Centigrade and pressureis at or near atmospheric.

Example 1 Production of Wild-Type and Mutant H-NOX Proteins

Wild-type and mutant H-NOX proteins were produced, expressed, andpurified using standard methods, essentially as described by Boon, E. M.et al. (2005). “Molecular Basis For NO Selectivity in Soluble GuanylateCyclase,” Nature Chemical Biology 1:53-59 and Karow, D. S. et al. (Aug.10, 2004). “Spectroscopic Characterization of The Soluble GuanylateCyclase-Like Heme Domains From Vibrio Cholerae And ThermoanaerobacterTengcongensis,” Biochemistry 43(31):10203-10211, which are both herebyincorporated by reference in their entireties, particularly with respectto the mutagenesis, expression, and purification of H-NOX proteins.Mutagenesis was performed using the QuickChange® protocol fromStrategene (La Jolla, Calif.). Expression of the proteins in cellculture and subsequent purification of the proteins was performed asdescribed by Karow, D. S. et al. (Aug. 10, 2004). “SpectroscopicCharacterization of The Soluble Guanylate Cyclase-Like Heme Domains FromVibrio Cholerae And Thermoanaerobacter Tengcongensis,” Biochemistry43(31):10203-10211.

Example 2 Characterization of Mutant H-NOX Proteins

Calculated K_(D) for NO: Ratio of k_(off) to k_(on)

To determine the calculated K_(D) for NO, the value for the k_(on) forNO for an H-NOX protein is assumed to be 710 μM⁻¹s⁻¹, and thedissociation rate for NO (k_(off) for an H-NOX protein with a6-coordinate Fe^(II)—NO complex or k₁ or k₂ for an H-NOX protein with a5-coordinate Fe^(II)—NO complex) is determined as described below.

k_(off), k₁, and k₂ (NO Dissociation Rates)

k_(off) Values for H-NOX Proteins with a 6-coordinate Fe^(II)—NO Complex

For an H-NOX protein with a 6-coordinate Fe^(II)—NO complex, the k_(off)for NO is calculated as described by Boon, E. M. et al., (August 2006),“Nitric Oxide Binding to Prokaryotic Homologs of the Solube GuanylateCyclase β1 H0NOX Domain,” J. Biol. Chem. 281(31): 21892-21902 and Boon,E. M. et al. (2005). “Molecular Basis For NO Selectivity in SolubleGuanylate Cyclase,” Nature Chemical Biology 1:53-59, which are eachhereby incorporated by reference in their entireties, particularly withrespect to the calculation of NO k_(off) for H-NOX proteins. Briefly,Fe^(II)—NO complexes of H-NOX protein (5 μM heme final concentration)diluted in anaerobic 50 mM triethanolamine, 50 mM NaCl, pH 7.5, bufferwere rapidly mixed with a saturated carbon monoxide and 30 mM (finalconcentration) dithionite trap (Na₂S₂O₄) in the same buffer (anaerobic)(Kharitonov, V. G. et al. (1997). Biochemistry 36:6814-6818 and Moore,E. G. et al. (1976). J. Biol. Chem. 251:2788-2794, which are each herebyincorporated by reference in their entireties, particularly with respectto the calculation of NO dissociation rates). It has been establishedpreviously that CO binding is not rate-limiting in these experiments(Kharitonov, V. G. et al. (1997) Biochemistry 36:6814-6818); this wasconfirmed in experiments using only 30 mM Na₂S₂O₄ without CO as a trap.Data were acquired by scanning periodically on a Cary 3Espectrophotometer equipped with a Neslab RTE-100 constant temperaturebath set to varying temperatures (0-70° C.) using a quartz cuvette witha size of 100 μL to 1 mL and a path-length of 1-cm (Cary 3E, Varian,Inc., Palo Alto, Calif.). The dissociation of NO from the heme wasmonitored as the formation of the Fe^(II)—CO complex at 423 nm.Difference spectra were calculated by subtracting the first scan fromeach subsequent scan. The NO dissociation rate was determined from theincrease in absorbance at 423 nm versus time and fit with a singleexponential of the form f(x)=A×(1−e^(−kx)) using Kaleidagraph 3.X(Synergy Software, Reading, Pa.). In particular, a single exponentialincrease in the concentration of heme-CO (due to CO binding from the NOtrap) can be described by equation 1:ΔA _(t) =ΔA _(T)(1−e ^(−k) ¹ ^(t))  (equation 1)

where ΔA_(t) is the change in signal amplitude at time t; ΔA_(T) is thetotal change in signal amplitude, and k₁ is the observed reaction rateconstant. Each experiment was performed a minimum of six times, and theresulting rates were averaged. The dissociation rates measured areindependent of CO and dithionite concentration (3, 30, and 300 mMdithionite were tested).

k₁ and k₂ Values for H-NOX Proteins with a 5-Coordinate Fe^(II)—NOComplex

For an H-NOX protein with a 5-coordinate Fe^(II)—NO complex, the k_(off)for NO is described by the k₁ for NO and the k₂ for NO, as described byWinger, J. A. et al., (January 2007) “Dissociation of Nitric Oxide fromSoluble Guanylate Cyclase and Heme-Nitric Oxide/Oxygen Binding DomainConstructs” J. Biol. Chem. 282(2): 897-907, which is hereby incorporatedby reference in its entirety, particularly with respect to thecalculation of NO k_(off), NO k₁, and NO k₂ for H-NOX proteins. Briefly,the dissociation of NO from the heme of H-NOX proteins with a5-coordinate Fe^(II)—NO complex was measured at 37 and 10° C. using theCO/dithionite trapping method described previously (Cary, S. P. L., etal. (2005) Proc. Natl. Acad. Sci. U S. A. 102: 13064-13069 andKharitonov, V. G. et al. (1997) Biochemistry 36:6814-6818, which areeach hereby incorporated by reference in their entireties, particularlywith respect to the calculation of NO dissociation rates). The trappingsolution was prepared as follows: a solution of sodium dithionite(Na₂S₂O₄) in 50 mM HEPES, pH 7.4, 50 mM NaCl was prepared in aTeflon-sealed Reacti-Vial (Pierce) using an anaerobic chamber (CoyLaboratory Products). The solution was removed from the anaerobicchamberand saturated with CO by bubbling the gas through the solution for 10minutes. H-NOX protein-NO complexes were formed by incubation withexcess DEA/NO (in 10 mM NaOH) at 25° C. in 50 mM HEPES, pH 7.4, 50 mMNaCl for 10 min. Complete conversion to the nitrosyl species wasverified by following the shift in the Soret maximum from 431 to 399 nm.H-NOX proteins were placed in a septum-sealed anaerobic cuvette (aquartz cuvette with a size of 100 μL to 1 mL and a path-length of 1-cm)and deoxygenated using an oxygen-scavenged gas train. A small amount ofDEA/NO (˜3 eq) was added just before deoxygenation to maintain thenitrosyl species (any remainder was subsequently destroyed by the largeexcess of Na₂S₂O₄ in the trapping solution). The head space of theanaerobic cuvette was replaced with CO, and the cuvette and trapsolutions were equilibrated at assay temperature for 1 minute. Thereaction was initiated by addition of CO/dithionite solution to theanaerobic cuvette with a Hamilton gas-tight syringe and mixing. Thefinal concentration of Na₂S₂O₄ in the reaction mixture was 30 mM. Finalprotein concentrations were 1.9 to 2.5 μM for β1(1-194), β1(1-385), andβ2(1-217), and 0.88 to 2.5 μM for sGC. Data collection was initiated 10seconds after trap addition. The reaction was monitored by electronicabsorption spectroscopy using a Cary 3E spectrophotometer equipped witha Neslab RTE-100 temperature controller (Cary 3E, Varian, Inc., PaloAlto, Calif.). Data were collected over the range of 380-450 nm at 909nm/min with a 1.5-nm data point interval. Spectra were recorded every 18seconds for 5 minutes, every 1 minute for 10 minutes, and every 2minutes thereafter for a total of 3 hours, or until the reaction wascomplete. A buffer base line was subtracted from each spectrum, andspectra were corrected for base-line drift by normalization to anisosbestic point at 410 nm. Difference spectra were obtained bysubtraction of the time 0 spectrum from all subsequent spectra. Valuesfor the change in absorbance at 423 nm (ΔA₄₂₃; β1(1-194) and β1(1-385))or 424 nm (ΔA₄₂₄; sGC and (β2(1-217)) were extracted from the differencespectra and plotted versus time to obtain dissociation time courses foreach experiment. Dissociation time courses were obtained in duplicate ortriplicate, and each experiment was repeated 2-5 times over severaldays. Generally, because of the relative difficulty in obtaining largeamounts of purified sGC, ΔA₄₂₄ values for full-length sGC, which areproportional to the experimental protein concentrations, were smallerthan for the heme domain constructs.

Curve fitting, data analysis, and figure generation were carried outusing Kaleidagraph 3.X (Synergy Software Reading, Pa.). The data fromeach dissociation experiment were fit to a double exponentials as shownin Equation 2 below to obtain observed rate constants.

In particular, equation 2 describes a two-exponential increase in theconcentration of heme-CO (due to CO binding from the NO trap):ΔA _(t) =ΔA ₁(1−e ^(−k) ¹ ^(t))+ΔA ₂(1−e ^(−k) ² ^(t))  (equation 2)where ΔA_(t) is the change in signal amplitude at time t; ΔA₁ and ΔA₂are the contributions of each exponential process to the total change insignal amplitude, and k₁ and k₁ are the observed rate constants for eachprocess.

The observed data are consistent with a model where dissociationproceeds from an initial equilibrium mixture of two 5-coordinate heme-NOcomplexes, as outlined in Scheme 1. Accordingly, k₁ corresponds to thedissociation of NO from the heme-NO_(5C) conformation, whereas k₂represents the observed rate of reaction, corresponding to k_(O)-k_(C),that is limited by the slower conversion from heme-NO NO*_(5C) toheme-NO_(5C).

k₁ and k₂ Values for H-NOX Proteins with Mixture of 5-Coordinate and6-Coordinate Fe^(II)—NO Complexes

For an H-NOX protein that contains a mixture of 5-coordinate and6-coordinate Fe^(II)—NO complexes, the k_(off) for NO is described bythe k₁ for NO and the k₂ for NO. The k₁ and the k₂ for NO are measuredas described above for H-NOX proteins with a 5-coordinate Fe^(II)—NOcomplex, as described by Winger, J. A. et al., (January 2007)“Dissociation of Nitric Oxide from Soluble Guanylate Cyclase andHeme-Nitric Oxide/Oxygen Binding Domain Constructs” J. Biol. Chem.282(2): 897-907, which is hereby incorporated by reference in itsentirety, particularly with respect to the calculation of NO k_(off), NOk₁, and NO k₂ for H-NOX proteins.

Calculated K_(D) for NO

For the calculated K_(D) for NO, the value for the k_(on) for NO for anH-NOX protein is assumed to be 710 μM⁻¹s⁻¹, which is a reported k_(on)for β1(1-385) that was measured at 4° C. and does not increasesignificantly at 37° C. (Zhao, et. al., (1999). “A Molecular Basis forNitric Oxide Sensing by Soluble Guanylate Cyclase,” PNAS.96:14753-14758, which is hereby incorporated by reference in itsentirety, particularly with respect to the calculation of NO k_(on) forH-NOX proteins). Thus, the calculated K_(D) for NO is determined bycalculating the ratio of either k_(off), k₁, or k₂ (measured asdescribed above) to k_(on) (assumed to be 710 μM⁻¹s⁻¹).

Kinetic K_(D) for O₂: Ratio of k_(off) to k_(on)

The kinetic K_(D) value for O₂ was determined for wild-type and mutantH-NOX proteins essentially as described by Boon, E. M. et al. (2005).“Molecular Basis For NO Selectivity in Soluble Guanylate Cyclase,”Nature Chemical Biology 1:53-59, which is hereby incorporated byreference in its entirety, particularly with respect to the measurementof O₂ association rates, O₂ dissociation rates, dissociation constantsfor O₂ binding, autoxidation rates, and NO dissociation rates.

k_(on) (O₂ Association Rate)

O₂ association to the heme was measured using flash photolysis at 20° C.It was not possible to flash off the Fe^(II)—O₂ complex as a result ofthe very fast geminate recombination kinetics; thus, the Fe^(II)—COcomplex was subjected to flash photolysis with laser light at 560 nm(Hewlett-Packard, Palo Alto, Calif.), producing the 5-coordinate Fe^(II)intermediate, to which the binding of molecular O₂ was followed atvarious wavelengths. Protein samples were made by anaerobic reductionwith 10 mM dithionite, followed by desalting on a PD-10 column(Millipore, Inc., Billerica, Mass.). The samples were then diluted to 20μM heme in 50 mM TEA, 50 mM NaCl, pH 7.5 buffer in acontrolled-atmosphere quartz cuvette, with a size of 100 μL to 1 mL anda path-length of 1-cm. CO gas was flowed over the headspace of thiscuvette for 10 minutes to form the Fe^(II)—CO complex, the formation ofwhich was verified by UV-visible spectroscopy (Soret maximum 423 nm).This sample was then either used to measure CO-rebinding kinetics afterflash photolysis while still under 1 atmosphere of CO gas, or it wasopened and stirred in air for 30 minutes to fully oxygenate the bufferbefore flash photolysis to watch O₂-rebinding events. O₂ association tothe heme was monitored at multiple wavelengths versus time. These traceswere fit with a single exponential using Igor Pro software (Wavemetrics,Inc., Oswego, Oreg.; latest 2005 version). This rate was independent ofobservation wavelength but dependent on O₂ concentration. UV-visiblespectroscopy was used throughout to confirm all the complexes andintermediates (Cary 3K, Varian, Inc. Palo Alto, Calif.). Transientabsorption data were collected using instruments described inDmochowski, I. J. et al. (Aug. 31, 2000). “Enantiomeric Discriminationof Ru-Substrates by Cytochrome P450cam,” J Inorg Biochem. 81(3):221-228,which is hereby incorporated by reference in its entirety, particularlywith respect to instrumentation. The instrument has a response time of20 ns, and the data are digitized at 200 megasamples s⁻¹.

k_(off) (O₂ Dissociation Rate)

To measure the k_(off), Fe^(II)—O₂ complexes of protein (5 μM heme),diluted in anaerobic 50 mM TEA, 50 mM NaCl, pH 7.5 buffer, were rapidlymixed with an equal volume of the same buffer (anaerobic) containingvarious concentrations of dithionite and/or saturating CO gas. Data wereacquired on a HI-TECH Scientific SF-61 stopped-flow spectrophotometerequipped with a Neslab RTE-100 constant-temperature bath set to 20° C.(TGK Scientific LTD., Bradford On Avon, United Kingdom). Thedissociation of O₂ from the heme was monitored as an increase in theabsorbance at 437 nm, a maximum in the Fe^(II)—Fe^(II)—O₂ differencespectrum, or 425 nm, a maximum in the Fe^(II)—Fe^(II)—CO differencespectrum. The final traces were fit to a single exponential using thesoftware that is part of the instrument. Each experiment was done aminimum of six times, and the resulting rates were averaged. Thedissociation rates measured are independent of dithionite concentration(100, 50, 25, 10, 5 and 2.5 mM dithionite were tested) and independentof saturating CO as a trap for the reduced species, both with andwithout 10 mM dithionite present.

Kinetic K_(D) for O₂

The kinetic K_(D) for O₂ is determined by calculating the ratio ofk_(off) to k_(on) using the measurements of k_(off) and k_(on) describedabove.

Calculated K_(D)

To measure the calculated K_(D), the values for the k_(off) and kineticK_(D) that were obtained as described above were graphed. A linearrelationship between k_(off) and kinetic K_(D) was defined by theequation (y=mx+b). k_(off) values were then interpolated along the lineto derive the calculated K_(D) using Excel: MAC 2004 (Microsoft,Redmond, Wash.). In the absence of a measured k_(on), this interpolationprovides a way to relate k_(off) to K_(D).

Rate of Autoxidation

To measure the rate of autoxidation, the protein samples wereanaerobically reduced; then diluted to 5 μM heme in aerobic 50 mM TEA,50 mM NaCl, pH 7.5 buffer. These samples were then incubated in a Cary3E spectrophotometer equipped with a Neslab RTE-100 constant-temperaturebath set to 37° C. and scanned periodically (Cary 3E, Varian, Inc., PaloAlto, Calif.). The rate of autoxidation was determined from thedifference between the maximum and minimum in the Fe^(III)—Fe^(II)difference spectrum plotted versus time and fit with a singleexponential using Excel: MAC 2004 (Microsoft, Redmond, Wash.).

Rate of Reaction with NO

NO reactivity was measured using purified proteins (Tt WT HNOX, Tt Y140HHNOX, and Homo sapiens hemoglobin (Hs Hb)) prepared at 2 μM in buffer Aand NO prepared at 200 μM in Buffer A (Buffer A: 50 mM Hepes, pH 7.5, 50mM NaCl). Data were acquired on a HI-TECH Scientific SF-61 stopped-flowspectrophotometer equipped with a Neslab RTE-100 constant-temperaturebath set to 20° C. (TGK Scientific LTD., Bradford On Avon, UnitedKingdom). The protein was rapidly mixed with NO in a 1:1 ratio with anintegration time of 0.00125 sec. The wavelengths of maximum change werefit to a single exponential using the software that is part of thespectrometer, essentially measuring the rate-limiting step of oxidationby NO. The end products of the reaction were ferric-NO for the HNOXproteins and ferric-aquo for Hs Hb.

p50 Measurements

If desired, the p50 value for mutant or wild-type H-NOX proteins can bemeasured as described by Guarnone, R. et al. (September/October 1995).“Performance Characteristics of Hemox-Analyzer For Assessment of TheHemoglobin Dissociation Curve,” Haematologica 80(5):426-430, which ishereby incorporated by reference in its entirety, particularly withrespect to the measurement of p50 values. The p50 value is determinedusing a HemOx analyzer. The measurement chamber starts at 0% oxygen andslowly is raised, incrementally, towards 100% oxygen. An oxygen probe inthe chamber measures the oxygen saturation %. A second probe (UV-Vislight) measures two wavelengths of absorption, tuned to the alpha andbeta peaks of the hemoprotein's (e.g., a protein such as H-NOX complexedwith heme) UV-Vis spectra. These absorption peaks increase linearly ashemoprotein binds oxygen. The percent change from unbound to 100% boundis then plotted against the % oxygen values to generate a curve. The p50is the point on the curve where 50% of the hemoprotein is bound tooxygen.

Specifically, the Hemox-Analyzer (TCS Scientific Corporation, New Hope,Pa.) determines the oxyhemoprotein dissociation curve (ODC) by exposing50 μL of blood or hemoprotein to an increasing partial pressure ofoxygen and deoxygenating it with nitrogen gas. A Clark oxygen electrodedetects the change in oxygen tension, which is recorded on the x-axis ofan x-y recorder. The resulting increase in oxyhemoprotein fraction issimultaneously monitored by dual-wavelength spectrophotometry at 560 nmand 576 nm and displayed on the y-axis. Blood samples are taken from theantemedial vein, anticoagulated with heparin, and kept at 4° C. on wetice until the assay. Fifty μL, of whole blood are diluted in 5 μL ofHemox-solution, a manufacturer-provided buffer that keeps the pH of thesolution at a value of 7.4±0.01. The sample-buffer is drawn into acuvette that is part of the Hemox-Analyzer and the temperature of themixture is equilibrated and brought to 37° C.; the sample is thenoxygenated to 100% with air. After adjustment of the pO₂ value thesample is deoxygenated with nitrogen; during the deoxygenation processthe curve is recorded on graph paper. The P50 value is extrapolated onthe x-axis as the point at which O₂ saturation is 50% using the softwarethat is part of the Hemox-Analyzer. The time required for a completerecording is approximately 30 minutes.

The p50 values for any of the H-NOX proteins can be compared to that ofhemoglobin as an indication of the relative affinity of the H-NOXprotein for O₂ compared to that of hemoglobin. Table 15 lists previouslyreported p50 values for hemoglobin.

TABLE 15 Hemoglobin variants and their reported oxygen affinities K_(D)Reference/ Name Modification (nM) p50 (mmHg) Manufacturer Hemoglobin~400 14 (stroma-free) Hemoglobin 27 (RBC's) Hemopure (HBOC- Bovine 36Biopure 201) polymerized Oxyglobin (HBOC- Bovine 54 Biopure 301polymerized Hemospan (MP4) Maleimide-  5 Sangart PEG Polyheme Pyridoxal28-30 Northfield Labs Hemolink 0-raffinose 40 Hemosol HemassistDiaspirin 32 BaxterViscosity Measurements

If desired, the viscosity of the H-NOX solutions can be measured using acone/plate rheometer (model Dy-III, Brookfield; Middleboro, Mass.) withthe CPE-40 cone spindle at a shear rate of 200/s. Solutions withviscosities between 1 and 4 centipoise (cP) administered in hemodilutionoxygen delivery experiments are reported as safe (Winslow, R. M. et al.(October 2004). “Comparison of PEG-Modified Albumin And Hemoglobin inExtreme Hemodilution in the Rat,” J Appl Physiol. 97(4):1527-1534, U.S.Pat. Nos. 6,974,795, and 6,432,918, which are each hereby incorporatedby reference in their entireties, particularly with respect to themeasurement of viscosity). Accordingly, in some embodiments, theviscosity of the H-NOX protein solution is between 1 and 4 cP.

Colloid Oncotic Pressure Measurements

If desired, the colloid oncotic pressure can be measured using a colloidosmometer according to the manufacturer's instructions (model 4420,Wescor; Logan, Utah). Exemplary methods to measure colloid oncoticpressure are described in Vandegriff, K. D. et al. (November 1997).“Colloid Osmotic Properties of Modified Hemoglobins: ChemicallyCross-Linked Versus Polyethylene Glycol Surface-Conjugated,” Biophys.Chem. 69(1):23-30, in the world-wide web at“anaesthesiamcq.com/FluidBook/f12_(—)4.php;” U.S. Pat. Nos. 6,974,795,and 6,432,918, which are each hereby incorporated by reference in theirentireties, particularly with respect to measuring colloid oncoticpressure. Solutions with colloid oncotic pressure between 20 and 50 mmHg administered in hemodilution oxygen delivery experiments are reportedas safe (Winslow, R. M. et al. (October 2004). “Comparison ofPEG-Modified Albumin And Hemoglobin in Extreme Hemodilution in the Rat,”J. Appl. Physiol. 97(4):1527-1534). Accordingly, in some embodiments,the colloid oncotic pressure of the H-NOX protein solution is between 20and 50 mm Hg.

Example 3 Heart Disease Models for NO Carrier H-NOX Mutants

Two animal models can be used to compare the efficacy of H-NOX proteinsas NO carriers to standard nitrate therapy. To compare the effects ofH-NOX proteins with authentic NO delivery with isosorbide dinitrate(ISDN) in a rat model of chronic cardiovascular disease, an adaptationof an established protocol (Shimamura, S. et al. (2006). J Vet Med SciVol. 68(3):213-7, which is hereby incorporated by reference in itsentirety, particularly with respect to models of cardiovascular disease)can be performed using male Wistar rats. To simulate cardiovascularhypertrophy, the abdominal aorta is constricted (abdominal aortaconstriction or “AC” model) via ventral abdominal laparotomy andapplication of a constriction tie over an inserted 21-gauge needle,which is then removed to permit uniform vessel constriction.Sham-operated rats undergo similar surgery, but without creation of AC.After surgery, the rats are randomly divided into treatment groups of 14animals per group (7 on drug and 7 on placebo), and allowed to recoverfor 7 days. Treatments per group (control groups are paired within eachtest case as placebo) are: (1) AC rats administered oral sr-ISDN orplacebo; (2) AC rats administered IV one or more wild-type or mutantH-NOX proteins described herein or placebo (e.g., an inactivated H-NOXprotein); (3) and (4) sham-operated rats treated as in (1) or (2),respectively. Treatments are once a day for 12 weeks, after which theanimals are sacrificed, and the hearts are excised for standardhistopathological analyses for the determination of cardiomyocytemorphology, fibrosis, collage deposition, ventricular diameter, aorticmorphology, and other standard analyses for assessing diseaseprogression or prevention.

To compare the efficacy of H-NOX proteins to that of ISDN in mediatinglong-term left ventricular remodeling following acute myocardialinfarction, a canine model, in which ISDN has shown some efficacy viachronic administration, is performed using a standard protocol (Bodh I.Jugdutt, MBChB, MSc; Mohammad I. Khan, MBBS (1994). Circulation 89(S)).For each experiment, forty healthy mongrel dogs (weight, 16 to 29 kg) ofeither sex are given a left lateral thoracotomy under general anesthesia(sodium pentobarbital, 30 mg/kg IV). Polyethylene catheters are insertedin the external jugular vein, internal carotid artery, and left atrium,filled with heparinized saline, and their ends exteriorized behind theneck. A silk ligature is placed around the mid left anterior descendingcoronary artery, between the first and second diagonal branches, andtied. Metal beads are sutured on the anterior, lateral, and posteriorepicardial surfaces in the short-axis plane at the mid left ventricularlevel for consistent echocardiographic orientation for serialtopography. The pericardium and chest are then closed. Penicillin (1million units) and streptomycin (1 g) are given intramuscularly, and thedogs are returned to their cages.

Two days after coronary artery ligation, the 70 healthy survivors arerandomized to nitrate therapy (n=10), H-NOX protein therapy (e.g., oneor more wild-type or mutant H-NOX proteins that optionally have beencharacterized in vitro using any of the assays described herein andoptionally have undergone optimization for toxicity and/orpharmacokinetics) (10), and matching control subgroups (no treatment,n=20): subgroup 1 (10 control, 10 nitrate), and subgroup 2 (10 control,10 H-NOX protein). The dogs are allowed free access to fluids, and noattempt is made to treat heart failure by fluid restriction orpharmacotherapy. At six weeks, the surviving dogs are anesthetized, andthe hearts are arrested in diastole with an overdose of intravenouspotassium chloride, excised, washed in normal saline solution, andweighed. Blood samples are taken for monitoring blood gases, hemograms,and electrolytes. Using standard procedures, the measurements duringhealing are made (such as ECG's, hemodynamics, etc.), and post-mortemanalyses include those measures described above for chronic heartfailure (e.g., collagen accumulation, myocyte morphology, etc.). TheH-NOX proteins that are as effective or more effective than ISDN (thestandard of care for nitrate-based therapies for acute and chronic heartfailure) in the myocardial infarction and/or the chronic AC modelexperiments are particularly useful for the treatment of myocardialinfarction and/or chronic AC. Such H-NOX proteins are expected to alsobe useful to treat other indications for which delivery of NO isbeneficial.

The foregoing examples and detailed description are offered by way ofillustration and not by way of limitation. All publications, patentapplications, and patents cited in this specification are hereinincorporated by reference as if each individual publication, patentapplication, or patent were specifically and individually indicated tobe incorporated by reference. Although the foregoing invention has beendescribed in some detail by way of illustration and example for purposesof clarity of understanding, it will be readily apparent to those ofordinary skill in the art in light of the teachings of this inventionthat certain changes and modifications may be made thereto withoutdeparting from the spirit or scope of the appended claims.

Unless defined otherwise, the meanings of all technical and scientificterms used herein are those commonly understood by one of skill in theart to which this invention belongs. One of skill in the art will alsoappreciate that any methods and materials similar or equivalent to thosedescribed herein can also be used to practice or test the invention.

For use herein, unless clearly indicated otherwise, use of the terms“a”, “an,” and the like refers to one or more.

Reference to “about” a value or parameter herein includes (anddescribes) embodiments that are directed to that value or parameter perse. For example, description referring to “about X” includes descriptionof “X.”

It is understood that aspect and embodiments of the invention describedherein include “comprising,” “consisting,” and “consisting essentiallyof” aspects and embodiments.

What is claimed as new and desired to be protected by Letters Patent ofthe United States is:
 1. A pharmaceutical blood gas NO carriercomposition comprising (i) a pharmaceutically effective amount of anH-NOX protein, wherein said H-NOX protein binds and delivers NO withminimal NO reactivity, wherein the H-NOX protein comprises a distalpocket mutation, and wherein the H-NOX protein does not comprise aguanylyl cyclase catalytic domain: and (ii) a pharmaceuticallyacceptable carrier.
 2. The pharmaceutical blood gas NO carriercomposition of claim 1, wherein the k_(off), k₁, or k₂ for NO of theH-NOX protein is between about 1×10⁻⁴s⁻¹ and about 0.012 s⁻¹ at 37° C.3. The pharmaceutical blood gas NO carrier composition of claim 1,wherein the k_(off), k₁, or k₂ for NO of the H-NOX protein is betweenabout 1×10⁻⁴s⁻¹ and about 10 s⁻¹ at 37° C., and wherein the NOreactivity of the H-NOX protein is less than about 700 s⁻¹.
 4. Thepharmaceutical blood gas NO carrier composition of claim 1, wherein thek_(off), k₁, or k₂ for NO of the H-NOX protein is between about1×10⁻⁴s⁻¹ and about 10 s⁻¹ at 37° C., and wherein the rate of hemeautoxidation of the H-NOX protein is less than about 1 h⁻¹ at 37° C. 5.The pharmaceutical blood gas NO carrier composition of claim 1, whereinthe O₂ dissociation constant of the H-NOX protein is at least about 1 μMat 37° C., and wherein the rate of heme autoxidation of the H-NOXprotein is less than about 1 h⁻¹ at 37° C.
 6. The pharmaceutical bloodgas NO carrier composition of claim 1, wherein the rate of hemeautoxidation of the H-NOX protein is less than about 1 h⁻¹ at 37° C.,and wherein the NO reactivity of the H-NOX protein is less than about700 s⁻¹.
 7. The pharmaceutical blood gas NO carrier composition of claim1, wherein the distal pocket mutation alters the NO dissociationconstant, the k_(off) for NO, the k₁ for NO, the k₂ for NO, the O₂dissociation constant, the NO stability, the rate of heme autoxidation,or any combination of two or more of the foregoing compared to that of acorresponding wild-type protein.
 8. The pharmaceutical blood gas NOcarrier composition of claim 1, wherein the H-NOX protein is a mammalianprotein or is derived from a mammalian protein.
 9. The pharmaceuticalblood gas NO carrier composition of claim 1, wherein the H-NOX proteinis a bacterial protein or is derived from a bacterial protein, whereinthe H-NOX protein is an insect protein or is derived from an insectprotein, or wherein the H-NOX protein is a worm protein or is derivedfrom a worm protein.
 10. The pharmaceutical blood gas NO carriercomposition of claim 1, comprising one or more liposomes ornanoparticles that comprise the H-NOX protein.
 11. The pharmaceuticalblood gas NO carrier composition of claim 1, wherein the H-NOX proteinis covalently bound to another molecule or moiety.
 12. Thepharmaceutical blood gas NO carrier composition of claim 11, wherein theH-NOX protein is covalently bound to polyethylene glycol.
 13. Thepharmaceutical blood gas NO carrier composition of claim 1, wherein theNO dissociation constant of the H-NOX protein is within 2 orders ofmagnitude of that of hemoglobin, and wherein the NO reactivity of theH-NOX protein is at least 10-fold lower than that of hemoglobin.
 14. Thepharmaceutical blood gas NO carrier composition of claim 1, wherein thek_(off), k₁, or k₂ for NO of the H-NOX protein is between about1×10⁻⁴s⁻¹ and about 10 s⁻¹ at 37° C., and wherein the O₂ dissociationconstant of the H-NOX protein is at least about 1 μM at 37° C.
 15. A kitcomprising (i) a pharmaceutical composition of an H-NOX protein, whereinsaid H-NOX protein binds and delivers NO with minimal NO reactivity,wherein the H-NOX protein comprises a distal pocket mutation, andwherein the H-NOX protein does not comprise a guanylyl cyclase catalyticdomain: and (ii) instructions for using the kit to deliver NO to anindividual.
 16. The kit of claim 15, wherein the k_(off), k₁, or k₂ forNO of the H-NOX protein is between about 1×10⁻⁴s⁻¹ and about 10 s⁻¹ at37° C., and wherein the O₂ dissociation constant of the H-NOX protein isat least about 1 μM at 37° C.
 17. The kit of claim 15, wherein the H-NOXprotein binds and delivers NO with minimal NO reactivity, and whereinthe NO dissociation constant of the H-NOX protein is within 2 orders ofmagnitude of that of hemoglobin, and wherein the NO reactivity of theH-NOX protein is at least 10-fold lower than that of hemoglobin.
 18. Amethod of delivering NO to an individual comprising administering to anindividual in need thereof an H-NOX protein in an amount sufficient todeliver an effective amount of NO to the individual, wherein said H-NOXprotein binds and delivers NO with minimal NO reactivity, wherein theH-NOX protein comprises a distal pocket mutation, and wherein the H-NOXprotein does not comprise a guanylyl cyclase catalytic domain.
 19. Themethod of claim 18, wherein the k_(off), k₁, or k₂ for NO of the H-NOXprotein is between about 1×10⁻⁴s⁻¹ and about 0.012 s⁻¹ at 37° C.
 20. Themethod of claim 18, wherein the k_(off), k₁, or k₂ for NO of the H-NOXprotein is between about 1×10⁻⁴s⁻¹ and about 10 s⁻⁴ at 37° C., andwherein the O₂ dissociation constant of the H-NOX protein is at leastabout 1 μM at 37° C.
 21. The method of claim 18, wherein the k_(off),k₁, or k₂ for NO of the H-NOX protein is between about 1×10⁻⁴s⁻¹ andabout 10 s⁻¹ at 37° C., and wherein the NO reactivity of the H-NOXprotein is less than about 700 s⁻¹.
 22. The method of claim 18, whereinthe O₂ dissociation constant of the H-NOX protein is at least about 1 μMat 37° C., and wherein the NO reactivity of the H-NOX protein is lessthan about 700 s⁻¹.
 23. The method of claim 18, wherein the k_(off), k₁,or k₂ for NO of the H-NOX protein is between about 1×10⁻⁴s⁻¹ and about10 s⁻¹ at 37° C., and wherein the rate of heme autoxidation of the H-NOXprotein is less than about 1 h⁻¹ at 37° C.
 24. The method of claim 18,wherein the H-NOX protein comprises at least one mutation that altersthe NO dissociation constant, the k_(off) for NO, the k₁ for NO, the k₂for NO, the O₂ dissociation constant, the NO stability, the rate of hemeautoxidation, or any combination of two or more of the foregoingcompared to that of a corresponding wild-type protein.
 25. The method ofclaim 18, wherein the H-NOX protein is a mammalian protein or is derivedfrom a mammalian protein.
 26. The method of claim 18, wherein the H-NOXprotein is a bacterial protein or is derived from a bacterial protein,wherein the H-NOX protein is an insect protein or is derived from aninsect protein, or wherein the H-NOX protein is a worm protein or isderived from a worm protein.
 27. The method of claim 18, wherein one ormore liposomes or nanoparticles comprise the H-NOX protein.
 28. Themethod of claim 18, wherein the H-NOX protein is covalently bound toanother molecule or moiety.
 29. The method of claim 28, wherein theH-NOX protein is covalently bound to polyethylene glycol.
 30. The methodof claim 18, wherein the individual is a human.
 31. The method of claim18, wherein the individual is suffering from or at risk for acardiovascular condition, hypertension, a condition exacerbated byhypertension, a vasoconstrictive condition, stroke, a functional NOdeficiency, heart failure, or renal failure.
 32. The method of claim 18,wherein the NO dissociation constant of the H-NOX protein is within 2orders of magnitude of that of hemoglobin, and wherein the NO reactivityof the H-NOX protein is at least 10-fold lower than that of hemoglobin.33. The method of claim 18, wherein the k_(off), k₁, or k₂ for NO of theH-NOX protein is between about 1×10⁻⁴s⁻¹ and about 10 s⁻¹ at 37° C., andwherein the O₂ dissociation constant of the H-NOX protein is at leastabout 1 μM at 37° C.